leetcode Binary Tree Postorder Traversal 的题目咨询

帘项小竹 2014-07-13 12:38:51
题目:
Given a binary tree, return the postorder traversal of its nodes' values.
For example:
Given binary tree {1,#,2,3},

1
\
2
/
3

return [3,2,1].
Note: Recursive solution is trivial, could you do it iteratively?
问:
请问为什么我这么写有问题。。。
-------------------------------------答题区-------------------------------------

/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
// #include<vector>
class Solution {
public:
vector<int> postorderTraversal(TreeNode *root) {
vector<int> iter;
postorderTraversal(root->left);
postorderTraversal(root->right);
iter.push_back(root->val);

}
};
报错:Submission Result: Runtime Error

Last executed input: {}
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brookmill 2014-07-13
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题目还提到了非递归的方法,可以参考这个 http://blog.csdn.net/sgbfblog/article/details/7773103
brookmill 2014-07-13
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递归的要点之一是必须有结束条件 if (root != NULL) { postorderTraversal(root->left); postorderTraversal(root->right); iter.push_back(root->val); }
赵4老师 2014-07-13
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仅供参考
#include <iostream>
#include <stack>
#include <queue>
#include <locale.h>
using namespace std;
typedef struct BiTNode {//二叉树结点
    char data;                      //数据
    struct BiTNode *lchild,*rchild; //左右孩子指针
} BiTNode,*BiTree;
int CreateBiTree(BiTree &T) {//按先序序列创建二叉树
    char data;
    scanf("%c",&data);//按先序次序输入二叉树中结点的值(一个字符),‘#’表示空树
    if (data == '#') {
        T = NULL;
    } else {
        T = (BiTree)malloc(sizeof(BiTNode));
        T->data = data;         //生成根结点
        CreateBiTree(T->lchild);//构造左子树
        CreateBiTree(T->rchild);//构造右子树
    }
    return 0;
}
void Visit(BiTree T) {//输出
    if (T->data != '#') {
        printf("%c ",T->data);
    }
}
void PreOrder(BiTree T) {//先序遍历
    if (T != NULL) {
        Visit(T);               //访问根节点
        PreOrder(T->lchild);    //访问左子结点
        PreOrder(T->rchild);    //访问右子结点
    }
}
void InOrder(BiTree T) {//中序遍历
    if (T != NULL) {
        InOrder(T->lchild);     //访问左子结点
        Visit(T);               //访问根节点
        InOrder(T->rchild);     //访问右子结点
    }
}
void PostOrder(BiTree T) {//后序遍历
    if (T != NULL) {
        PostOrder(T->lchild);   //访问左子结点
        PostOrder(T->rchild);   //访问右子结点
        Visit(T);               //访问根节点
    }
}
void PreOrder2(BiTree T) {//先序遍历(非递归)
//访问T->data后,将T入栈,遍历左子树;遍历完左子树返回时,栈顶元素应为T,出栈,再先序遍历T的右子树。
    stack<BiTree> stack;
    BiTree p = T;//p是遍历指针
    while (p || !stack.empty()) {   //栈不空或者p不空时循环
        if (p != NULL) {
            stack.push(p);          //存入栈中
            printf("%c ",p->data);  //访问根节点
            p = p->lchild;          //遍历左子树
        } else {
            p = stack.top();        //退栈
            stack.pop();
            p = p->rchild;          //访问右子树
        }
    }
}
void InOrder2(BiTree T) {//中序遍历(非递归)
//T是要遍历树的根指针,中序遍历要求在遍历完左子树后,访问根,再遍历右子树。
//先将T入栈,遍历左子树;遍历完左子树返回时,栈顶元素应为T,出栈,访问T->data,再中序遍历T的右子树。
    stack<BiTree> stack;
    BiTree p = T;//p是遍历指针
    while (p || !stack.empty()) {   //栈不空或者p不空时循环
        if (p != NULL) {
            stack.push(p);          //存入栈中
            p = p->lchild;          //遍历左子树
        } else {
            p = stack.top();        //退栈,访问根节点
            printf("%c ",p->data);
            stack.pop();
            p = p->rchild;          //访问右子树
        }
    }
}

typedef struct BiTNodePost{
    BiTree biTree;
    char tag;
} BiTNodePost,*BiTreePost;
void PostOrder2(BiTree T) {//后序遍历(非递归)
    stack<BiTreePost> stack;
    BiTree p = T;//p是遍历指针
    BiTreePost BT;
    while (p != NULL || !stack.empty()) {//栈不空或者p不空时循环
        while (p != NULL) {//遍历左子树
            BT = (BiTreePost)malloc(sizeof(BiTNodePost));
            BT->biTree = p;
            BT->tag = 'L';//访问过左子树
            stack.push(BT);
            p = p->lchild;
        }
        while (!stack.empty() && (stack.top())->tag == 'R') {//左右子树访问完毕访问根节点
            BT = stack.top();
            stack.pop();//退栈
            printf("%c ",BT->biTree->data);
        }
        if (!stack.empty()) {//遍历右子树
            BT = stack.top();
            BT->tag = 'R';//访问过右子树
            p = BT->biTree;
            p = p->rchild;
        }
    }
}

void LevelOrder(BiTree T) {//层次遍历
    if (T == NULL) return;
    BiTree p = T;
    queue<BiTree> queue;//队列
    queue.push(p);//根节点入队
    while (!queue.empty()) {    //队列不空循环
        p = queue.front();      //对头元素出队
        printf("%c ",p->data);  //访问p指向的结点
        queue.pop();            //退出队列
        if (p->lchild != NULL) {//左子树不空,将左子树入队
            queue.push(p->lchild);
        }
        if (p->rchild != NULL) {//右子树不空,将右子树入队
            queue.push(p->rchild);
        }
    }
}
int main() {
    BiTree T;

    setlocale(LC_ALL,"chs");
    CreateBiTree(T);

    printf("先序遍历        :");PreOrder  (T);printf("\n");
    printf("先序遍历(非递归):");PreOrder2 (T);printf("\n");
                                               printf("\n");
    printf("中序遍历        :");InOrder   (T);printf("\n");
    printf("中序遍历(非递归):");InOrder2  (T);printf("\n");
                                               printf("\n");
    printf("后序遍历        :");PostOrder (T);printf("\n");
    printf("后序遍历(非递归):");PostOrder2(T);printf("\n");
                                               printf("\n");
    printf("层次遍历        :");LevelOrder(T);printf("\n");

    return 0;
}
//ABC##DE#G##F###
//先序遍历        :A B C D E G F
//先序遍历(非递归):A B C D E G F
//
//中序遍历        :C B E G D F A
//中序遍历(非递归):C B E G D F A
//
//后序遍历        :C G E F D B A
//后序遍历(非递归):C G E F D B A
//
//层次遍历        :A B C D E F G
//

///       A
///      /
///     B
///    / \
///   C   D
///      / \
///     E   F
///      \
///       G
帘项小竹 2014-07-13
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引用 1 楼 brookmill 的回复:
递归的要点之一是必须有结束条件 if (root != NULL) { postorderTraversal(root->left); postorderTraversal(root->right); iter.push_back(root->val); }
没有用啊,加上去还是没有办法accepted
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# [LeetCode](https://leetcode.com/problemset/algorithms/) ![Language](https://img.shields.io/badge/language-Python%20%2F%20C++%2011-orange.svg) [![License](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE.md) ![Progress](https://img.shields.io/badge/progress-468%20%2F%20468-ff69b4.svg) Up to date (2016-12-18), there are `447` Algorithms / `13` Database / `4` Shell / `4` Draft questions on [LeetCode Online Judge](https://leetcode.com/). The number of questions is increasing recently. Here is the classification of all `468` questions. For more questions and solutions, you can see my [LintCode](https://github.com/kamyu104/LintCode) repository. I'll keep updating for full summary and better solutions. Stay tuned for updates. (Notes: "馃摉" means you need to subscribe to [LeetCode premium membership](https://leetcode.com/subscribe/) for the access to premium questions.) ## Algorithms * [Bit Manipulation](https://github.com/kamyu104/LeetCode#bit-manipulation) * [Array](https://github.com/kamyu104/LeetCode#array) * [String](https://github.com/kamyu104/LeetCode#string) * [Linked List](https://github.com/kamyu104/LeetCode#linked-list) * [Stack](https://github.com/kamyu104/LeetCode#stack) * [Queue](https://github.com/kamyu104/LeetCode#queue) * [Heap](https://github.com/kamyu104/LeetCode#heap) * [Tree](https://github.com/kamyu104/LeetCode#tree) * [Hash Table](https://github.com/kamyu104/LeetCode#hash-table) * [Data Structure](https://github.com/kamyu104/LeetCode#data-structure) * [Math](https://github.com/kamyu104/LeetCode#math) * [Two Pointers](https://github.com/kamyu104/LeetCode#two-pointers) * [Sort](https://github.com/kamyu104/LeetCode#sort) * [Recursion](https://github.com/kamyu104/LeetCode#recursion) * [Binary Search](https://github.com/kamyu104/LeetCode#binary-search) * [Binary Search Tree](https://github.com/kamyu104/LeetCode#binary-search-tree) * [Breadth-First Search](https://github.com/kamyu104/LeetCode#breadth-first-search) * [Depth-First Search](https://github.com/kamyu104/LeetCode#depth-first-search) * [Backtracking](https://github.com/kamyu104/LeetCode#backtracking) * [Dynamic Programming](https://github.com/kamyu104/LeetCode#dynamic-programming) * [Greedy](https://github.com/kamyu104/LeetCode#greedy) * [Design](https://github.com/kamyu104/LeetCode#design) ## Database * [SQL](https://github.com/kamyu104/LeetCode#sql) ## Shell * [Shell Script](https://github.com/kamyu104/LeetCode#shell-script) ## Bit Manipulation | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 136 | [Single Number](https://leetcode.com/problems/single-number/) | [C++](./C++/single-number.cpp) [Python](./Python/single-number.py) | _O(n)_ | _O(1)_ | Easy ||| 137 | [Single Number II](https://leetcode.com/problems/single-number-ii/) | [C++](./C++/single-number-ii.cpp) [Python](./Python/single-number-ii.py) | _O(n)_ | _O(1)_ | Medium ||| 190 | [Reverse Bits](https://leetcode.com/problems/reverse-bits/) | [C++](./C++/reverse-bits.cpp) [Python](./Python/reverse-bits.py) | _O(1)_ | _O(1)_ | Easy ||| 191 |[Number of 1 Bits](https://leetcode.com/problems/number-of-1-bits/) | [C++](./C++/number-of-1-bits.cpp) [Python](./Python/number-of-1-bits.py) | _O(1)_ | _O(1)_ | Easy ||| 201 | [Bitwise AND of Numbers Range](https://leetcode.com/problems/bitwise-and-of-numbers-range/) | [C++](./C++/bitwise-and-of-numbers-range.cpp) [Python](./Python/bitwise-and-of-numbers-range.py) | _O(1)_ | _O(1)_ | Medium || 231 | [Power of Two](https://leetcode.com/problems/power-of-two/) | [C++](./C++/power-of-two.cpp) [Python](./Python/power-of-two.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | [C++](./C++/single-number-iii.cpp) [Python](./Python/single-number-iii.py) | _O(n)_ | _O(1)_ | Medium || 268| [Missing Number](https://leetcode.com/problems/missing-number/) | [C++](./C++/missing-number.cpp) [Python](./Python/missing-number.py) | _O(n)_ | _O(1)_ | Medium | LintCode || 318| [Maximum Product of Word Lengths](https://leetcode.com/problems/maximum-product-of-word-lengths/) | [C++](./C++/maximum-product-of-word-lengths.cpp) [Python](./Python/maximum-product-of-word-lengths.py) | _O(n)_ ~ _O(n^2)_ | _O(n)_ | Medium || Bit Manipulation, Counting Sort, Pruning| 342 | [Power of Four](https://leetcode.com/problems/power-of-four/) | [C++](./C++/power-of-four.cpp) [Python](./Python/power-of-four.py) | _O(1)_ | _O(1)_ | Easy | | 371 | [Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/) | [C++](./C++/sum-of-two-integers.cpp) [Python](./Python/sum-of-two-integers.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 389 | [Find the Difference](https://leetcode.com/problems/find-the-difference/) | [C++](./C++/find-the-difference.cpp) [Python](./Python/find-the-difference.py) | _O(n)_ | _O(1)_ | Easy | | 393 | [UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/) | [C++](./C++/utf-8-validation.cpp) [Python](./Python/utf-8-validation.py) | _O(n)_ | _O(1)_ | Medium | | 401 | [Binary Watch](https://leetcode.com/problems/binary-watch/) | [C++](./C++/binary-watch.cpp) [Python](./Python/binary-watch.py) | _O(1)_ | _O(1)_ | Easy | | 411 | [Minimum Unique Word Abbreviation](https://leetcode.com/problems/minimum-unique-word-abbreviation/) | [C++](./C++/minimum-unique-word-abbreviation.cpp) [Python](./Python/minimum-unique-word-abbreviation.py) | _O(2^n)_ | _O(n)_ | Hard | 馃摉 | 421 | [Maximum XOR of Two Numbers in an Array](https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array/) | [C++](./C++/maximum-xor-of-two-numbers-in-an-array.cpp) [Python](./Python/maximum-xor-of-two-numbers-in-an-array.py) | _O(n)_ | _O(1)_ | Medium || 461 | [Hamming Distance](https://leetcode.com/problems/hamming-distance/) | [C++](./C++/hamming-distance.cpp) [Python](./Python/hamming-distance.py) | _O(1)_ | _O(1)_ | Easy || 462 | [Minimum Moves to Equal Array Elements II](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/) | [C++](./C++/minimum-moves-to-equal-array-elements-ii.cpp) [Python](./Python/minimum-moves-to-equal-array-elements-ii.py) | _O(n)_ on average | _O(1)_ | Medium || 477 | [Total Hamming Distance](https://leetcode.com/problems/total-hamming-distance/) | [C++](./C++/total-hamming-distance.cpp) [Python](./Python/total-hamming-distance.py) | _O(n)_ | _O(1)_ | Medium || ## Array | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 15 | [3 Sum](https://leetcode.com/problems/3sum/) | [C++](./C++/3sum.cpp) [Python](./Python/3sum.py) | _O(n^2)_ | _O(1)_ | Medium || Two Pointers 16 | [3 Sum Closest](https://leetcode.com/problems/3sum-closest/) | [C++](./C++/3sum-closest.cpp) [Python](./Python/3sum-closest.py) | _O(n^2)_ | _O(1)_ | Medium || Two Pointers 18| [4 Sum](https://leetcode.com/problems/4sum/) | [C++](./C++/4sum.cpp) [Python](./Python/4sum.py) | _O(n^3)_ | _O(1)_ | Medium || Two Pointers 26 | [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)| [C++](./C++/remove-duplicates-from-sorted-array.cpp) [Python](./Python/remove-duplicates-from-sorted-array.py) | _O(n)_ | _O(1)_ | Easy || Two Pointers 27 | [Remove Element](https://leetcode.com/problems/remove-element/) | [C++](./C++/remove-element.cpp) [Python](./Python/remove-element.py) | _O(n)_ | _O(1)_ | Easy || 31 | [Next Permutation](https://leetcode.com/problems/next-permutation/)| [C++](./C++/next-permutation.cpp) [Python](./Python/next-permutation.py) | _O(n)_ | _O(1)_ | Medium || Tricky 41 | [First Missing Positive](https://leetcode.com/problems/first-missing-positive/)| [C++](./C++/first-missing-positive.cpp) [Python](./Python/first-missing-positive.py) | _O(n)_ | _O(1)_ | Hard || Tricky 48 | [Rotate Image](https://leetcode.com/problems/rotate-image/) | [C++](./C++/rotate-image.cpp) [Python](./Python/rotate-image.py) | _O(n^2)_ | _O(1)_ | Medium || 54 | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [C++](./C++/spiral-matrix.cpp) [Python](./Python/spiral-matrix.py) | _O(m * n)_ | _O(1)_ | Medium || 59 | [Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/) | [C++](./C++/spiral-matrix-ii.cpp) [Python](./Python/spiral-matrix-ii.py) | _O(n^2)_ | _O(1)_ | Medium || 66 | [Plus One](https://leetcode.com/problems/plus-one/) | [C++](./C++/plus-one.cpp) [Python](./Python/plus-one.py) | _O(n)_ | _O(1)_ | Easy || 73 | [Set Matrix Zeroes](https://leetcode.com/problems/set-matrix-zeroes/) | [C++](./C++/set-matrix-zeroes.cpp) [Python](./Python/set-matrix-zeroes.py) | _O(m * n)_ | _O(1)_ | Medium || 80 | [Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)| [C++](./C++/remove-duplicates-from-sorted-array-ii.cpp) [Python](./Python/remove-duplicates-from-sorted-array-ii.py) | _O(n)_ | _O(1)_ | Medium || Two Pointers 118 | [Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)| [C++](./C++/pascals-triangle.cpp) [Python](./Python/pascals-triangle.py) | _O(n^2)_ | _O(1)_ | Easy || 119 | [Pascal's Triangle II](https://leetcode.com/problems/pascals-triangle-ii/)| [C++](./C++/pascals-triangle-ii.cpp) [Python](./Python/pascals-triangle-ii.py) | _O(n^2)_ | _O(1)_ | Easy || 121 | [Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [C++](./C++/best-time-to-buy-and-sell-stock.cpp) [Python](./Python/best-time-to-buy-and-sell-stock.py) | _O(n)_ | _O(1)_ | Easy || 128 | [Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)| [C++](./C++/longest-consecutive-sequence.cpp) [Python](./Python/longest-consecutive-sequence.py) | _O(n)_ | _O(n)_ | Hard || Tricky 157 | [Read N Characters Given Read4](https://leetcode.com/problems/read-n-characters-given-read4/) | [C++](./C++/read-n-characters-given-read4.cpp) [Python](./Python/read-n-characters-given-read4.py) | _O(n)_ | _O(1)_ | Easy |馃摉| 158 | [Read N Characters Given Read4 II - Call multiple times](https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/) | [C++](./C++/read-n-characters-given-read4-ii-call-multiple-times.cpp) [Python](./Python/read-n-characters-given-read4-ii-call-multiple-times.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 163 | [Missing Ranges](https://leetcode.com/problems/missing-ranges/)| [C++](./C++/missing-ranges.cpp) [Python](./Python/missing-ranges.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 169 | [Majority Element](https://leetcode.com/problems/majority-element/) | [C++](./C++/majority-element.cpp) [Python](./Python/majority-element.py) | _O(n)_ | _O(1)_ | Easy | 189 | [Rotate Array](https://leetcode.com/problems/rotate-array/) | [C++](./C++/rotate-array.cpp) [Python](./Python/rotate-array.py) | _O(n)_ | _O(1)_ | Easy || 209 | [Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/) | [C++](./C++/minimum-size-subarray-sum.cpp) [Python](./Python/minimum-size-subarray-sum.py) | _O(n)_ | _O(1)_ | Medium | | Binary Search 215 | [Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/) | [C++](./C++/kth-largest-element-in-an-array.cpp) [Python](./Python/kth-largest-element-in-an-array.py)| _O(n)_ ~ _O(n^2)_ | _O(1)_ | Medium | EPI| 228 | [Summary Ranges](https://leetcode.com/problems/summary-ranges/) | [C++](./C++/summary-ranges.cpp) [Python](./Python/summary-ranges.py)| _O(n)_ | _O(1)_ | Medium | | 229 | [Majority Element II](https://leetcode.com/problems/majority-element-ii/) | [C++](./C++/majority-element-ii.cpp) [Python](./Python/majority-element-ii.py) | _O(n)_ | _O(1)_ | Medium | | 238 | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/) | [C++](./C++/product-of-array-except-self.cpp) [Python](./Python/product-of-array-except-self.py) | _O(n)_ | _O(1)_ | Medium | LintCode | 240 | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [C++](./C++/search-a-2d-matrix-ii.cpp) [Python](./Python/search-a-2d-matrix-ii.py) | _O(m + n)_ | _O(1)_ | Medium | EPI, LintCode | 243| [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/) | [C++](./C++/shortest-word-distance.cpp) [Python](./Python/shortest-word-distance.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 245| [Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/) | [C++](./C++/shortest-word-distance-iii.cpp) [Python](./Python/shortest-word-distance-iii.py) | _O(n)_ | _O(1)_ | Medium |馃摉|| 251| [Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector/) | [C++](./C++/flatten-2d-vector.cpp) [Python](./Python/flatten-2d-vector.py) | _O(1)_ | _O(1)_ | Medium |馃摉|| 277| [Find the Celebrity](https://leetcode.com/problems/find-the-celebrity/) | [C++](./C++/find-the-celebrity.cpp) [Python](./Python/find-the-celebrity.py) | _O(n)_ | _O(1)_ | Medium |馃摉, EPI || 289| [Game of Life](https://leetcode.com/problems/game-of-life/) | [C++](./C++/game-of-life.cpp) [Python](./Python/game-of-life.py) | _O(m * n)_ | _O(1)_ | Medium ||| 293| [Flip Game](https://leetcode.com/problems/flip-game/) | [C++](./C++/flip-game.cpp) [Python](./Python/flip-game.py) | _O(n * (c+1))_ | _O(1)_ | Easy |馃摉|| 296| [Best Meeting Point](https://leetcode.com/problems/best-meeting-point/) | [C++](./C++/best-meeting-point.cpp) [Python](./Python/best-meeting-point.py) | _O(m * n)_ | _O(m + n)_ | Hard |馃摉|| 311| [Sparse Matrix Multiplication](https://leetcode.com/problems/sparse-matrix-multiplication/) | [C++](./C++/sparse-matrix-multiplication.cpp) [Python](./Python/sparse-matrix-multiplication.py) | _O(m * n * l)_ | _O(m * l)_ | Medium |馃摉|| 334| [Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/) | [C++](./C++/increasing-triplet-subsequence.cpp) [Python](./Python/increasing-triplet-subsequence.py) | _O(n)_ | _O(1)_ | Medium ||| 370| [Range Addition](https://leetcode.com/problems/range-addition/) | [C++](./C++/range-addition.cpp) [Python](./Python/range-addition.py) | _O(k + n)_ | _O(1)_ | Medium |馃摉|| 384| [Shuffle an Array](https://leetcode.com/problems/shuffle-an-array/) | [C++](./C++/shuffle-an-array.cpp) [Python](./Python/shuffle-an-array.py) | _O(n)_ | _O(n)_ | Medium | EPI || 396| [Rotate Function](https://leetcode.com/problems/rotate-function/) | [C++](./C++/rotate-function.cpp) [Python](./Python/rotate-function.py) | _O(n)_ | _O(1)_ | Easy ||| 412| [Fizz Buzz](https://leetcode.com/problems/fizz-buzz/) | [C++](./C++/fizz-buzz.cpp) [Python](./Python/fizz-buzz.py) | _O(n)_ | _O(1)_ | Easy ||| 414| [Third Maximum Number](https://leetcode.com/problems/third-maximum-number/) | [C++](./C++/third-maximum-number.cpp) [Python](./Python/third-maximum-number.py) | _O(n)_ | _O(1)_ | Easy ||| 419| [Battleships in a Board](https://leetcode.com/problems/battleships-in-a-board/) | [C++](./C++/battleships-in-a-board.cpp) [Python](./Python/battleships-in-a-board.py) | _O(m * n)_ | _O(1)_ | Medium ||| 422| [Valid Word Square](https://leetcode.com/problems/valid-word-square/) | [C++](./C++/valid-word-square.cpp) [Python](./Python/valid-word-square.py) | _O(m * n)_ | _O(1)_ | Easy |馃摉|| 442| [Find All Duplicates in an Array](https://leetcode.com/problems/find-all-duplicates-in-an-array/) | [C++](./C++/find-all-duplicates-in-an-array.cpp) [Python](./Python/find-all-duplicates-in-an-array.py) | _O(n)_ | _O(1)_ | Medium ||| 448| [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/) | [C++](./C++/find-all-numbers-disappeared-in-an-array.cpp) [Python](./Python/find-all-numbers-disappeared-in-an-array.py) | _O(n)_ | _O(1)_ | Easy ||| ## String | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 5| [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [C++](./C++/longest-palindromic-substring.cpp) [Python](./Python/longest-palindromic-substring.py) | _O(n)_ | _O(n)_ | Medium || `Manacher's Algorithm` 6| [ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/) | [C++](./C++/zigzag-conversion.cpp) [Python](./Python/zigzag-conversion.py) | _O(n)_ | _O(1)_ | Easy || 8| [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [C++](./C++/string-to-integer-atoi.cpp) [Python](./Python/string-to-integer-atoi.py) | _O(n)_ | _O(1)_ | Easy || 14| [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/) | [C++](./C++/longest-common-prefix.cpp) [Python](./Python/longest-common-prefix.py) | _O(n * k)_ | _O(1)_ | Easy || 28| [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [C++](./C++/implement-strstr.cpp) [Python](./Python/implement-strstr.py) | _O(n + k)_ | _O(k)_ | Easy || `KMP Algorithm` 38| [Count and Say](https://leetcode.com/problems/count-and-say/) | [C++](./C++/count-and-say.cpp) [Python](./Python/count-and-say.py)| _O(n * 2^n)_ | _O(2^n)_ | Easy || 43| [Multiply Strings](https://leetcode.com/problems/multiply-strings/) | [C++](./C++/multiply-strings.cpp) [Python](./Python/multiply-strings.py) | _O(m * n)_ | _O(m + n)_ | Medium || 58| [Length of Last Word](https://leetcode.com/problems/length-of-last-word/) | [C++](./C++/length-of-last-word.cpp) [Python](./Python/length-of-last-word.py) | _O(n)_ | _O(1)_ | Easy || 67| [Add Binary](https://leetcode.com/problems/add-binary/) | [C++](./C++/add-binary.cpp) [Python](./Python/add-binary.py) | _O(n)_ | _O(1)_ | Easy || 68| [Text Justification](https://leetcode.com/problems/text-justification/) | [C++](./C++/text-justification.cpp) [Python](./Python/text-justification.py) | _O(n)_ | _O(1)_ | Hard || 125| [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/) | [C++](./C++/valid-palindrome.cpp) [Python](./Python/valid-palindrome.py) | _O(n)_ | _O(1)_ | Easy || 151| [Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/) | [C++](./C++/reverse-words-in-a-string.cpp) [Python](./Python/reverse-words-in-a-string.py) | _O(n)_ | _O(1)_ | Medium || 161| [One Edit Distance](https://leetcode.com/problems/one-edit-distance/) | [C++](./C++/one-edit-distance.cpp) [Python](./Python/one-edit-distance.py) | _O(m + n)_ | _O(1)_ | Medium |馃摉 | 165| [Compare Version Numbers](https://leetcode.com/problems/compare-version-numbers/) | [C++](./C++/compare-version-numbers.cpp) [Python](./Python/compare-version-numbers.py) | _O(n)_ | _O(1)_ | Easy || 186| [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/) |[C++](./C++/reverse-words-in-a-string-ii.cpp) [Python](./Python/reverse-words-in-a-string-ii.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 214| [Shortest Palindrome](https://leetcode.com/problems/shortest-palindrome/) | [C++](./C++/shortest-palindrome.cpp) [Python](./Python/shortest-palindrome.py) | _O(n)_ | _O(n)_ | Hard || `KMP Algorithm` `Manacher's Algorithm` 242| [Valid Anagram](https://leetcode.com/problems/valid-anagram/)| [C++](./C++/valid-anagram.cpp) [Python](./Python/valid-anagram.py) | _O(n)_ | _O(1)_ | Easy | LintCode | 271| [Encode and Decode Strings](https://leetcode.com/problems/encode-and-decode-strings/) | [C++](./C++/encode-and-decode-strings.cpp) [Python](./Python/encode-and-decode-strings.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 273| [Integer to English Words](https://leetcode.com/problems/integer-to-english-words/) | [C++](./C++/integer-to-english-words.cpp) [Python](./Python/integer-to-english-words.py) | _O(logn)_ | _O(1)_ | Hard | | 306| [Addictive Number](https://leetcode.com/problems/additive-number/) | [C++](./C++/additive-number.cpp) [Python](./Python/additive-number.py) | _O(n^3)_ | _O(n)_ | Medium | | 383| [Ransom Note](https://leetcode.com/problems/ransom-note/) | [C++](./C++/ransom-note.cpp) [Python](./Python/ransom-note.py) | _O(n)_ | _O(1)_ | Easy | EPI | 405| [Convert a Number to Hexadecimal](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) | [C++](./C++/convert-a-number-to-hexadecimal.cpp) [Python](./Python/convert-a-number-to-hexadecimal.py) | _O(n)_ | _O(1)_ | Easy | | 408| [Valid Word Abbreviation](https://leetcode.com/problems/valid-word-abbreviation/) | [C++](./C++/valid-word-abbreviation.cpp) [Python](./Python/valid-word-abbreviation.py) | _O(n)_ | _O(1)_ | Easy | 馃摉 | 415| [Add Strings](https://leetcode.com/problems/add-strings/) | [C++](./C++/add-strings.cpp) [Python](./Python/add-strings.py) | _O(n)_ | _O(1)_ | Easy | | 420| [Strong Password Checker](https://leetcode.com/problems/strong-password-checker/) | [C++](./C++/strong-password-checker.cpp) [Python](./Python/strong-password-checker.py) | _O(n)_ | _O(1)_ | Hard | | 434| [Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string/) | [C++](./C++/number-of-segments-in-a-string.cpp) [Python](./Python/number-of-segments-in-a-string.py) | _O(n)_ | _O(1)_ | Easy | | 459| [Repeated Substring Pattern](https://leetcode.com/problems/repeated-substring-pattern/) | [C++](./C++/repeated-substring-pattern.cpp) [Python](./Python/repeated-substring-pattern.py) | _O(n)_ | _O(n)_ | Easy || `KMP Algorithm` | 468| [Validate IP Address](https://leetcode.com/problems/validate-ip-address/) | [C++](./C++/validate-ip-address.cpp) [Python](./Python/validate-ip-address.py) | _O(1)_ | _O(1)_ | Medium | | ## Linked List | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 2| [Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [C++](./C++/add-two-numbers.cpp) [Python](./Python/add-two-numbers.py) | _O(n)_ | _O(1)_ | Medium || 21| [Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| [C++](./C++/merge-two-sorted-lists.cpp) [Python](./Python/merge-two-sorted-lists.py) | _O(n)_ | _O(1)_ | Easy || 23| [Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/) | [C++](./C++/merge-k-sorted-lists.cpp) [Python](./Python/merge-k-sorted-lists.py) | _O(nlogk)_| _O(1)_| Hard | | Heap, Divide and Conquer 24| [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)| [C++](./C++/swap-nodes-in-pairs.cpp) [Python](./Python/swap-nodes-in-pairs.py) | _O(n)_ | _O(1)_ | Easy || 25| [Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/)| [C++](./C++/reverse-nodes-in-k-group.cpp) [Python](./Python/reverse-nodes-in-k-group.py) | _O(n)_ | _O(1)_ | Hard || 61| [Rotate List](https://leetcode.com/problems/rotate-list/)| [C++](./C++/rotate-list.cpp) [Python](./Python/rotate-list.py) | _O(n)_ | _O(1)_ | Medium || 82| [Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/)| [C++](./C++/remove-duplicates-from-sorted-list-ii.cpp) [Python](./Python/remove-duplicates-from-sorted-list-ii.py) | _O(n)_ | _O(1)_ | Medium || 83| [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/)| [C++](./C++/remove-duplicates-from-sorted-list.cpp) [Python](./Python/remove-duplicates-from-sorted-list.py) | _O(n)_ | _O(1)_ | Easy || 92| [Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii/)| [C++](./C++/reverse-linked-list-ii.cpp) [Python](./Python/reverse-linked-list-ii.py) | _O(n)_ | _O(1)_ | Medium || 138| [Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/) | [C++](./C++/copy-list-with-random-pointer.cpp) [Python](./Python/copy-list-with-random-pointer.py) | _O(n)_ | _O(1)_ | Hard || 160| [Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/)| [C++](./C++/intersection-of-two-linked-lists.cpp) [Python](./Python/intersection-of-two-linked-lists.py) | _O(m + n)_ | _O(1)_ | Easy || 203| [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/)| [C++](./C++/remove-linked-list-elements.cpp) [Python](./Python/remove-linked-list-elements.py) | _O(n)_ | _O(1)_ | Easy || 206| [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [C++](./C++/reverse-linked-list.cpp) [Python](./Python/reverse-linked-list.py) | _O(n)_ | _O(1)_ | Easy || 234| [Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)| [C++](./C++/palindrome-linked-list.cpp) [Python](./Python/palindrome-linked-list.py) | _O(n)_ | _O(1)_ | Easy || 237| [Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/)| [C++](./C++/delete-node-in-a-linked-list.cpp) [Python](./Python/delete-node-in-a-linked-list.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 328| [Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list/)| [C++](./C++/odd-even-linked-list.cpp) [Python](./Python/odd-even-linked-list.py) | _O(n)_ | _O(1)_ | Medium | | 369| [Plus One Linked List](https://leetcode.com/problems/plus-one-linked-list/)| [C++](./C++/plus-one-linked-list.cpp) [Python](./Python/plus-one-linked-list.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | Two Pointers | 445| [Add Two Numbers II](https://leetcode.com/problems/add-two-numbers-ii/)| [C++](./C++/add-two-numbers-ii.cpp) [Python](./Python/add-two-numbers-ii.py) | _O(m + n)_ | _O(m + n)_ | Medium ||| ## Stack | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 20| [Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [C++](./C++/valid-parentheses.cpp) [Python](./Python/valid-parentheses.py) | _O(n)_ | _O(n)_ | Easy || 32| [Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/)| [C++](./C++/longest-valid-parentheses.cpp) [Python](./Python/longest-valid-parentheses.py) | _O(n)_ | _O(1)_ | Hard || 71| [Simplify Path](https://leetcode.com/problems/simplify-path/)| [C++](./C++/simplify-path.cpp) [Python](./Python/simplify-path.py) | _O(n)_ | _O(n)_ | Medium || 84| [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/) | [C++](./C++/largest-rectangle-in-histogram.cpp) [Python](./Python/largest-rectangle-in-histogram.py) | _O(n)_ | _O(n)_ | Hard || Ascending Stack, DP 85| [Maximal Rectangle](https://leetcode.com/problems/maximal-rectangle/)| [C++](./C++/maximal-rectangle.cpp) [Python](./Python/maximal-rectangle.py)| _O(m * n)_ | _O(n)_ | Hard | EPI | Ascending Stack 101| [Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)| [C++](./C++/symmetric-tree.cpp) [Python](./Python/symmetric-tree.py) | _O(n)_ | _O(h)_ | Easy || 150| [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)| [C++](./C++/evaluate-reverse-polish-notation.cpp) [Python](./Python/evaluate-reverse-polish-notation.py)| _O(n)_| _O(n)_| Medium || 155| [Min Stack](https://leetcode.com/problems/min-stack/) | [C++](./C++/min-stack.cpp) [Python](./Python/min-stack.py) | _O(n)_ | _O(1)_ | Easy || 173| [Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/) | [C++](./C++/binary-search-tree-iterator.cpp) [Python](./Python/binary-search-tree-iterator.py) | _O(1)_| _O(h)_| Medium || 224| [Basic Calculator](https://leetcode.com/problems/basic-calculator/) | [C++](./C++/basic-calculator.cpp) [Python](./Python/basic-calculator.py) | _O(n)_| _O(n)_| Hard || 227| [Basic Calculator II](https://leetcode.com/problems/basic-calculator-ii/) | [C++](./C++/basic-calculator-ii.cpp) [Python](./Python/basic-calculator-ii.py) | _O(n)_| _O(n)_| Medium || 232| [Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/) | [C++](./C++/implement-queue-using-stacks.cpp) [Python](./Python/implement-queue-using-stacks.py) | _O(1), amortized_| _O(n)_| Easy | EPI, LintCode | 255| [Verify Preorder Sequence in Binary Search Tree](https://leetcode.com/problems/verify-preorder-sequence-in-binary-search-tree/) | [C++](./C++/verify-preorder-sequence-in-binary-search-tree.cpp) [Python](./Python/verify-preorder-sequence-in-binary-search-tree.py) | _O(n)_| _O(1)_| Medium |馃摉|| 272| [Closest Binary Search Tree Value II](https://leetcode.com/problems/closest-binary-search-tree-value-ii/) | [C++](./C++/closest-binary-search-tree-value-ii.cpp) [Python](./Python/closest-binary-search-tree-value-ii.py) | _O(h + k)_| _O(h)_| Hard |馃摉|| 331| [Verify Preorder Serialization of a Binary Tree](https://leetcode.com/problems/verify-preorder-serialization-of-a-binary-tree/) | [C++](./C++/verify-preorder-serialization-of-a-binary-tree.cpp) [Python](./Python/verify-preorder-serialization-of-a-binary-tree.py) | _O(n)_| _O(1)_| Medium ||| 341| [Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator/)| [C++](./C++/flatten-nested-list-iterator.cpp) [Python](./Python/flatten-nested-list-iterator.py) | _O(n)_ | _O(h)_ | Medium |馃摉| Iterator | 385| [Mini Parser](https://leetcode.com/problems/mini-parser/)| [C++](./C++/mini-parser.cpp) [Python](./Python/mini-parser.py) | _O(n)_ | _O(h)_ | Medium ||| 394| [Decode String](https://leetcode.com/problems/decode-string/)| [C++](./C++/decode-string.cpp) [Python](./Python/decode-string.py) | _O(n)_ | _O(h)_ | Medium ||| 439| [Ternary Expression Parser](https://leetcode.com/problems/ternary-expression-parser/) | [C++](./C++/ternary-expression-parser.cpp) [Python](./Python/ternary-expression-parser.py) | _O(n)_ | _O(1)_ | Medium |馃摉| 456| [132 Pattern](https://leetcode.com/problems/132-pattern/) | [C++](./C++/132-pattern.cpp) [Python](./Python/132-pattern.py) | _O(n)_ | _O(n)_ | Medium || ## Queue | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 239| [Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/)| [C++](./C++/sliding-window-maximum.cpp) [Python](./Python/sliding-window-maximum.py) | _O(n)_ | _O(k)_ | Hard | EPI, LintCode | 281| [Zigzag Iterator](https://leetcode.com/problems/zigzag-iterator/)| [C++](./C++/zigzag-iterator.cpp) [Python](./Python/zigzag-iterator.py) | _O(n)_ | _O(k)_ | Medium |馃摉|| 346| [Moving Average from Data Stream](https://leetcode.com/problems/moving-average-from-data-stream/)| [C++](./C++/moving-average-from-data-stream.cpp) [Python](./Python/moving-average-from-data-stream.py) | _O(1)_ | _O(w)_ | Easy |馃摉|| ## Heap | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 264| [Ugly Number II](https://leetcode.com/problems/ugly-number-ii/) | [C++](./C++/ugly-number-ii.cpp) [Python](./Python/ugly-number-ii.py) | _O(n)_ | _O(1)_ | Medium | CTCI, LintCode | BST, Heap | 295| [Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/) | [C++](./C++/find-median-from-data-stream.cpp) [Python](./Python/find-median-from-data-stream.py) | _O(nlogn)_ | _O(n)_ | Hard | EPI, LintCode | BST, Heap | 313| [Super Ugly Number](https://leetcode.com/problems/super-ugly-number/) | [C++](./C++/super-ugly-number.cpp) [Python](./Python/super-ugly-number.py) | _O(n * k)_ | _O(n + k)_ | Medium || BST, Heap | 358| [Rearrange String k Distance Apart](https://leetcode.com/problems/rearrange-string-k-distance-apart/)| [C++](./C++/rearrange-string-k-distance-apart.cpp) [Python](./Python/rearrange-string-k-distance-apart.py) | _O(n)_ | _O(n)_ | Hard |馃摉| Greedy, Heap | 373 | [Find K Pairs with Smallest Sums](https://leetcode.com/problems/find-k-pairs-with-smallest-sums/) | [C++](./C++/find-k-pairs-with-smallest-sums.cpp) [Python](./Python/find-k-pairs-with-smallest-sums.py) | _O(k * log(min(n, m, k)))_ | _O(min(n, m, k))_ | Medium ||| 378 | [Kth Smallest Element in a Sorted Matrix](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/) | [C++](./C++/kth-smallest-element-in-a-sorted-matrix.cpp) [Python](./Python/kth-smallest-element-in-a-sorted-matrix.py) | _O(k * log(min(n, m, k)))_ | _O(min(n, m, k))_ | Medium | LintCode || 407 | [Trapping Rain Water II](https://leetcode.com/problems/trapping-rain-water-ii/) | [C++](./C++/trapping-rain-water-ii.cpp) [Python](./Python/trapping-rain-water-ii.py) | _O(m * n * (logm + logn))_ | _O(m * n)_ | Hard | LintCode || ## Tree | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 94 | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/) | [C++](./C++/binary-tree-inorder-traversal.cpp) [Python](./Python/binary-tree-inorder-traversal.py) | _O(n)_| _O(1)_| Medium || `Morris Traversal` | 99 | [Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/) | [C++](./C++/recover-binary-search-tree.cpp) [Python](./Python/recover-binary-search-tree.py) | _O(n)_| _O(1)_| Hard || `Morris Traversal` 144 | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/) | [C++](./C++/binary-tree-preorder-traversal.cpp) [Python](./Python/binary-tree-preorder-traversal.py) | _O(n)_| _O(1)_| Medium || `Morris Traversal` 145 | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/) | [C++](./C++/binary-tree-postorder-traversal.cpp) [Python](./Python/binary-tree-postorder-traversal.py) | _O(n)_| _O(1)_| Hard || `Morris Traversal` 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/) | [C++](./C++/implement-trie-prefix-tree.cpp) [Python](./Python/implement-trie-prefix-tree.py) | _O(n)_ | _O(1)_ | Medium || Trie 211 | [Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/) | [C++](./C++/add-and-search-word-data-structure-design.cpp) [Python](./Python/add-and-search-word-data-structure-design.py) | _O(min(n, h))_ | _O(min(n, h))_ | Medium || Trie, DFS 226| [Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/) | [C++](./C++/invert-binary-tree.cpp) [Python](./Python/invert-binary-tree.py) | _O(n)_ | _O(h)_, _O(w)_ | Easy || 297 | [Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) | [C++](./C++/serialize-and-deserialize-binary-tree.cpp) [Python](./Python/serialize-and-deserialize-binary-tree.py) | _O(n)_ | _O(h)_ | Hard | LintCode | DFS 307 | [Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/) | [C++](./C++/range-sum-query-mutable.cpp) [Python](./Python/range-sum-query-mutable.py) | ctor: _O(n)_, update: _O(logn)_, query: _O(logn)_ | _O(n)_ | Medium | LintCode | DFS, Segment Tree, BIT 308 | [Range Sum Query 2D - Mutable](https://leetcode.com/problems/range-sum-query-2d-mutable/) | [C++](./C++/range-sum-query-2d-mutable.cpp) [Python](./Python/range-sum-query-2d-mutable.py) | ctor: _O(m * n)_, update: _O(logm + logn)_, query: _O(logm + logn)_ | _O(m * n)_ | Hard | 馃摉 | DFS, Segment Tree, BIT 315|[Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/)| [C++](./C++/count-of-smaller-numbers-after-self.cpp) [Python](./Python/count-of-smaller-numbers-after-self.py)| _O(nlogn)_ | _O(n)_ | Hard | LintCode | BST, BIT, Divide and Conquer | ## Hash Table | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 1| [Two Sum](https://leetcode.com/problems/two-sum/) | [C++](./C++/two-sum.cpp) [Python](./Python/two-sum.py) | _O(n)_ | _O(n)_ | Easy || 3| [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C++](./C++/longest-substring-without-repeating-characters.cpp) [Python](./Python/longest-substring-without-repeating-characters.py) | _O(n)_ | _O(1)_ | Medium || 30| [Substring with Concatenation of All Words](https://leetcode.com/problems/substring-with-concatenation-of-all-words/) | [C++](./C++/substring-with-concatenation-of-all-words.cpp) [Python](./Python/substring-with-concatenation-of-all-words.py) | _O(m * n * k)_ | _O(n * k)_ | Hard || 36| [Valid Sudoku](https://leetcode.com/problems/valid-sudoku/) | [C++](./C++/valid-sudoku.cpp) [Python](./Python/valid-sudoku.py) | _O(9^2)_ | _O(9)_ | Easy || 49| [Group Anagrams](https://leetcode.com/problems/anagrams/) | [C++](./C++/anagrams.cpp) [Python](./Python/anagrams.py) | _O(n * glogg)_ | _O(n)_ | Medium || 76| [Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/) | [C++](./C++/minimum-window-substring.cpp) [Python](./Python/minimum-window-substring.py) | _O(n)_ | _O(k)_ | Hard || 149| [Max Points on a Line](https://leetcode.com/problems/max-points-on-a-line/) | [C++](./C++/max-points-on-a-line.cpp) [Python](./Python/max-points-on-a-line.py) | _O(n^2)_ | _O(n)_ | Hard || 159| [Longest Substring with At Most Two Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/)| [C++](./C++/longest-substring-with-at-most-two-distinct-characters.cpp) [Python](./Python/longest-substring-with-at-most-two-distinct-characters.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 170| [Two Sum III - Data structure design](https://leetcode.com/problems/two-sum-iii-data-structure-design/) | [C++](./C++/two-sum-iii-data-structure-design.cpp) [Python](./Python/two-sum-iii-data-structure-design.py) | _O(n)_ | _O(n)_ | Easy | 馃摉 | 187| [Repeated DNA Sequences](https://leetcode.com/problems/repeated-dna-sequences/) | [Python](./Python/repeated-dna-sequences.py) | _O(n)_ | _O(n)_ | Medium || 202| [Happy Number](https://leetcode.com/problems/happy-number/) | [C++](./C++/happy-number.cpp) [Python](./Python/happy-number.py) | _O(k)_ | _O(k)_ | Easy || 204| [Count Primes](https://leetcode.com/problems/count-primes/) | [C++](./C++/count-primes.cpp) [Python](./Python/count-primes.py) | _O(n)_ | _O(n)_ | Easy || 205| [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) | [C++](./C++/isomorphic-strings.cpp) [Python](./Python/isomorphic-strings.py) | _O(n)_ | _O(1)_ | Easy || 217| [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | [C++](./C++/contains-duplicate.cpp) [Python](./Python/contains-duplicate.py) | _O(n)_ | _O(n)_ | Easy || 219| [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/) | [C++](./C++/contains-duplicate-ii.cpp) [Python](./Python/contains-duplicate-ii.py) | _O(n)_ | _O(n)_ | Easy || 244| [Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii/) | [C++](./C++/shortest-word-distance-ii.cpp) [Python](./Python/shortest-word-distance-ii.py) | ctor: _O(n)_, lookup: _O(a + b)_ | _O(n)_ | Medium |馃摉|| 246| [Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) | [C++](./C++/strobogrammatic-number.cpp) [Python](./Python/strobogrammatic-number.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 249| [Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/) | [C++](./C++/group-shifted-strings.cpp) [Python](./Python/group-shifted-strings.py) | _O(nlogn)_ | _O(n)_ | Easy |馃摉|| 266| [Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation/) | [C++](./C++/palindrome-permutation.cpp) [Python](./Python/palindrome-permutation.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 288| [Unique Word Abbreviation](https://leetcode.com/problems/unique-word-abbreviation/) | [C++](./C++/unique-word-abbreviation.cpp) [Python](./Python/unique-word-abbreviation.py) | ctor: _O(n)_, lookup: _O(1)_ | _O(k)_ | Easy |馃摉|| 290| [Word Pattern](https://leetcode.com/problems/word-pattern/) | [C++](./C++/word-pattern.cpp) [Python](./Python/word-pattern.py) | _O(n)_ | _O(c)_ | Easy | variant of [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) || 299| [Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/) | [C++](./C++/bulls-and-cows.cpp) [Python](./Python/bulls-and-cows.py) | _O(n)_ | _O(1)_ | Easy ||| 305| [Number of Islands II](https://leetcode.com/problems/number-of-islands-ii/) | [C++](./C++/number-of-islands-ii.cpp) [Python](./Python/number-of-islands-ii.py) | _O(k)_ | _O(k)_| Hard | LintCode, 馃摉 | Union Find 314| [Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/) | [C++](./C++/binary-tree-vertical-order-traversal.cpp) [Python](./Python/binary-tree-vertical-order-traversal.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | BFS 323| [Number of Connected Components in an Undirected Graph](https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/) | [C++](./C++/number-of-connected-components-in-an-undirected-graph.cpp) [Python](./Python/number-of-connected-components-in-an-undirected-graph.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | Union Find 325| [Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/) | [C++](./C++/maximum-size-subarray-sum-equals-k.cpp) [Python](./Python/maximum-size-subarray-sum-equals-k.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | 336| [Palindrome Pairs](https://leetcode.com/problems/palindrome-pairs/) | [C++](./C++/palindrome-pairs.cpp) [Python](./Python/palindrome-pairs.py) | _O(n * k^2)_ | _O(n * k)_ | Hard | | | 340| [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)| [C++](./C++/longest-substring-with-at-most-k-distinct-characters.cpp) [Python](./Python/longest-substring-with-at-most-k-distinct-characters.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 356| [Line Reflection](https://leetcode.com/problems/line-reflection/) | [C++](./C++/line-reflection.cpp) [Python](./Python/line-reflection.py) | _O(n)_| _O(n)_| Medium |馃摉| Hash, Two Pointers | 387| [First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/) | [C++](./C++/first-unique-character-in-a-string.cpp) [Python](./Python/first-unique-character-in-a-string.py) | _O(n)_| _O(n)_| Easy ||| 388| [Longest Absolute File Path](https://leetcode.com/problems/longest-absolute-file-path/) | [C++](./C++/longest-absolute-file-path.cpp) [Python](./Python/longest-absolute-file-path.py) | _O(n)_| _O(d)_| Medium || Stack | 409| [Longest Palindrome](https://leetcode.com/problems/longest-palindrome/) | [C++](./C++/longest-palindrome.cpp) [Python](./Python/longest-palindrome.py) | _O(n)_| _O(1)_| Easy ||| 424| [Longest Repeating Character Replacement](https://leetcode.com/problems/longest-repeating-character-replacement/) | [C++](./C++/longest-repeating-character-replacement.cpp) [Python](./Python/longest-repeating-character-replacement.py) | _O(n)_| _O(1)_| Medium ||| 438| [Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/) | [C++](./C++/find-all-anagrams-in-a-string.cpp) [Python](./Python/find-all-anagrams-in-a-string.py) | _O(n)_ | _O(1)_ | Easy || 447| [Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs/) | [C++](./C++/number-of-boomerangs.cpp) [Python](./Python/number-of-boomerangs.py) | _O(n^2)_ | _O(n)_ | Easy || 454| [4Sum II](https://leetcode.com/problems/4sum-ii/) | [C++](./C++/4sum-ii.cpp) [Python](./Python/4sum-ii.py) | _O(n^2)_ | _O(n^2)_ | Medium || 473| [Matchsticks to Square](https://leetcode.com/problems/matchsticks-to-square/) | [C++](./C++/matchsticks-to-square.cpp) [Python](./Python/matchsticks-to-square.py) | _O(n * s * 2^n)_ | _O(n * (2^n + s))_ | Medium || ## Data Structure | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 146| [LRU Cache](https://leetcode.com/problems/lru-cache/) | [C++](./C++/lru-cache.cpp) [Python](./Python/lru-cache.py) | _O(1)_ | _O(k)_ | Hard || 225| [Implement Stack using Queues](https://leetcode.com/problems/implement-stack-using-queues/) | [C++](./C++/implement-stack-using-queues.cpp) [Python](./Python/implement-stack-using-queues.py) | push: _O(n)_, pop: _O(1)_, top: _O(1)_ | _O(n)_ | Easy || ## Math | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 7| [Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [C++](./C++/reverse-integer.cpp) [Python](./Python/reverse-integer.py) | _O(1)_ | _O(1)_ | Easy || 9| [Palindrome Number](https://leetcode.com/problems/palindrome-number/) | [C++](./C++/palindrome-number.cpp) [Python](./Python/palindrome-number.py) | _O(1)_ | _O(1)_ | Easy || 12| [Integer to Roman](https://leetcode.com/problems/integer-to-roman/) | [C++](./C++/integer-to-roman.cpp) [Python](./Python/integer-to-roman.py) | _O(n)_ | _O(1)_ | Medium || 13| [Roman to Integer](https://leetcode.com/problems/roman-to-integer/) | [C++](./C++/roman-to-integer.cpp) [Python](./Python/roman-to-integer.py) | _O(n)_ | _O(1)_ | Easy || 29| [Divide Two Integers](https://leetcode.com/problems/divide-two-integers/) | [C++](./C++/divide-two-integers.cpp) [Python](./Python/divide-two-integers.py) | _O(1)_ | _O(1)_ | Medium || 50| [Pow(x, n)](https://leetcode.com/problems/powx-n/) | [C++](./C++/powx-n.cpp) [Python](./Python/powx-n.py) | _O(1)_ | _O(1)_ | Medium || 60| [Permutation Sequence](https://leetcode.com/problems/permutation-sequence/) | [C++](./C++/permutation-sequence.cpp) [Python](./Python/permutation-sequence.py) | _O(n^2)_ | _O(n)_ | Medium || `Cantor Ordering` 65| [Valid Number](https://leetcode.com/problems/valid-number/) | [C++](./C++/valid-number.cpp) [Python](./Python/valid-number.py) | _O(n)_ | _O(1)_ | Hard || `Automata` 89| [Gray Code](https://leetcode.com/problems/gray-code/) | [C++](./C++/gray-code.cpp) [Python](./Python/gray-code.py) | _O(2^n)_ | _O(1)_ | Medium || 166| [Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/) | [C++](./C++/fraction-to-recurring-decimal.cpp) [Python](./Python/fraction-to-recurring-decimal.py) | _O(logn)_ | _O(1)_ | Medium || 168| [Excel Sheet Column Title](https://leetcode.com/problems/excel-sheet-column-title/) | [C++](./C++/excel-sheet-column-title.cpp) [Python](./Python/excel-sheet-column-title.py) | _O(logn)_ | _O(1)_ | Easy || 171| [Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/) | [C++](./C++/excel-sheet-column-number.cpp) [Python](./Python/excel-sheet-column-number.py) | _O(n)_ | _O(1)_ | Easy || 172| [Factorial Trailing Zeroes](https://leetcode.com/problems/factorial-trailing-zeroes/) | [C++](./C++/factorial-trailing-zeroes.cpp) [Python](./Python/factorial-trailing-zeroes.py) | _O(1)_ | _O(1)_ | Easy || 223| [Rectangle Area](https://leetcode.com/problems/rectangle-area/) | [C++](./C++/rectangle-area.cpp) [Python](./Python/rectangle-area.py) | _O(1)_ | _O(1)_ | Easy || 233| [Number of Digit One](https://leetcode.com/problems/number-of-digit-one/) | [C++](./C++/number-of-digit-one.cpp) [Python](./Python/number-of-digit-one.py) | _O(1)_ | _O(1)_ | Hard | CTCI, LintCode| 248| [Strobogrammatic Number III](https://leetcode.com/problems/strobogrammatic-number-iii/) | [C++](./C++/strobogrammatic-number-iii.cpp) [Python](./Python/strobogrammatic-number-iii.py) | _O(5^(n/2))_ | _O(n)_ | Hard |馃摉|| 258| [Add Digits](https://leetcode.com/problems/add-digits/) | [C++](./C++/add-digits.cpp) [Python](./Python/add-digits.py) | _O(1)_ | _O(1)_ | Easy ||| 263| [Ugly Number](https://leetcode.com/problems/ugly-number/) | [C++](./C++/ugly-number.cpp) [Python](./Python/ugly-number.py) | _O(1)_ | _O(1)_ | Easy ||| 292| [Nim Game](https://leetcode.com/problems/nim-game/) | [C++](./C++/nim-game.cpp) [Python](./Python/nim-game.py) | _O(1)_ | _O(1)_ | Easy | LintCode || 319 | [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/) | [C++](./C++/bulb-switcher.cpp) [Python](./Python/bulb-switcher.py) | _O(1)_ | _O(1)_ | Medium ||| 326 | [Power of Three](https://leetcode.com/problems/power-of-three/) | [C++](./C++/power-of-three.cpp) [Python](./Python/power-of-three.py) | _O(1)_ | _O(1)_ | Easy ||| 335 | [Self Crossing](https://leetcode.com/problems/self-crossing/) | [C++](./C++/self-crossing.cpp) [Python](./Python/self-crossing.py) | _O(n)_ | _O(1)_ | Hard ||| 338 | [Counting Bits](https://leetcode.com/problems/counting-bits/) | [C++](./C++/counting-bits.cpp) [Python](./Python/counting-bits.py) | _O(n)_ | _O(n)_ | Medium ||| 343 | [Integer Break](https://leetcode.com/problems/integer-break/) | [C++](./C++/integer-break.cpp) [Python](./Python/integer-break.py) | _O(logn)_ | _O(1)_ | Medium || Tricky, DP | 365 | [Water and Jug Problem](https://leetcode.com/problems/water-and-jug-problem/) | [C++](./C++/water-and-jug-problem.cpp) [Python](./Python/water-and-jug-problem.py) | _O(logn)_ | _O(1)_ | Medium || Euclidean Algorithm | 372 | [Super Pow](https://leetcode.com/problems/super-pow/) | [C++](./C++/super-pow.cpp) [Python](./Python/super-pow.py) | _O(n)_ | _O(1)_ | Medium ||| 382 | [Linked List Random Node](https://leetcode.com/problems/linked-list-random-node/) | [C++](./C++/linked-list-random-node.cpp) [Python](./Python/linked-list-random-node.py) | _O(n)_ | _O(1)_ | Medium || `Reservoir Sampling` | 386 | [Lexicographical Numbers](https://leetcode.com/problems/lexicographical-numbers/) | [C++](./C++/lexicographical-numbers.cpp) [Python](./Python/lexicographical-numbers.py) | _O(n)_ | _O(1)_ | Medium ||| 390 | [Elimination Game](https://leetcode.com/problems/elimination-game/) | [C++](./C++/elimination-game.cpp) [Python](./Python/elimination-game.py) | _O(logn)_ | _O(1)_ | Medium || 391 | [Perfect Rectangle](https://leetcode.com/problems/perfect-rectangle/) | [C++](./C++/perfect-rectangle.cpp) [Python](./Python/perfect-rectangle.py) | _O(n)_ | _O(n)_ | Hard | | 398 | [Random Pick Index](https://leetcode.com/problems/random-pick-index/) | [C++](./C++/random-pick-index.cpp) [Python](./Python/random-pick-index.py) | _O(n)_ | _O(1)_ | Medium || `Reservoir Sampling` | 400 | [Nth Digit](https://leetcode.com/problems/nth-digit/) | [C++](./C++/nth-digit.cpp) [Python](./Python/nth-digit.py) | _O(logn)_ | _O(1)_ | Easy ||| 413 | [Arithmetic Slices](https://leetcode.com/problems/arithmetic-slices/) | [C++](./C++/arithmetic-slices.cpp) [Python](./Python/arithmetic-slices.py) | _O(n)_ | _O(1)_ | Medium ||| 423 | [Reconstruct Original Digits from English](https://leetcode.com/problems/reconstruct-original-digits-from-english/) | [C++](./C++/reconstruct-original-digits-from-english.cpp) [Python](./Python/reconstruct-original-digits-from-english.py) | _O(n)_ | _O(1)_ | Medium | [GCJ2016 - Round 1B](https://code.google.com/codejam/contest/11254486/dashboard#s=p0)|| 441 | [Arranging Coins](https://leetcode.com/problems/arranging-coins/) | [C++](./C++/arranging-coins.cpp) [Python](./Python/arranging-coins.py) | _O(nlogn)_ | _O(1)_ | Easy || Binary Search| 453 | [Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/) | [C++](./C++/minimum-number-of-arrows-to-burst-balloons.cpp) [Python](./Python/minimum-number-of-arrows-to-burst-balloons.py) | _O(n)_ | _O(1)_ | Easy ||| 458 | [Poor Pigs](https://leetcode.com/problems/poor-pigs/) | [C++](./C++/poor-pigs.cpp) [Python](./Python/poor-pigs.py) | _O(n)_ | _O(1)_ | Easy ||| 469 | [Convex Polygon](https://leetcode.com/problems/convex-polygon/) | [C++](./C++/convex-polygon.cpp) [Python](./Python/convex-polygon.py) | _O(n)_ | _O(1)_ | Medium |馃摉|| ## Sort | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 56| [Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [C++](./C++/merge-intervals.cpp) [Python](./Python/merge-intervals.py) | _O(nlogn)_ | _O(1)_ | Hard || 57| [Insert Interval](https://leetcode.com/problems/insert-interval/)| [C++](./C++/insert-interval.cpp) [Python](./Python/insert-interval.py) | _O(n)_ | _O(1)_ | Hard || 75| [Sort Colors](https://leetcode.com/problems/sort-colors/) | [C++](./C++/sort-colors.cpp) [Python](./Python/sort-colors.py) | _O(n)_ | _O(1)_ | Medium || Tri Partition 88| [Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array/)| [C++](./C++/merge-sorted-array.cpp) [Python](./Python/merge-sorted-array.py) | _O(n)_ | _O(1)_ | Easy || 147| [Insertion Sort List](https://leetcode.com/problems/insertion-sort-list/)|[C++](./C++/insertion-sort-list.cpp) [Python](./Python/insertion-sort-list.py) | _O(n^2)_ | _O(1)_ | Medium || 148| [Sort List](https://leetcode.com/problems/sort-list/) | [C++](./C++/sort-list.cpp) [Python](./Python/sort-list.py) | _O(nlogn)_ | _O(logn)_ | Medium || 164| [Maximum Gap](https://leetcode.com/problems/maximum-gap/) | [C++](./C++/maximum-gap.cpp) [Python](./Python/maximum-gap.py)| _O(n)_ | _O(n)_ | Hard || Tricky 179| [Largest Number](https://leetcode.com/problems/largest-number/) | [C++](./C++/largest-number.cpp) [Python](./Python/largest-number.py) | _O(nlogn)_ | _O(1)_ | Medium || 218| [The Skyline Problem](https://leetcode.com/problems/the-skyline-problem/) | [C++](./C++/the-skyline-problem.cpp) [Python](./Python/the-skyline-problem.py) | _O(nlogn)_ | _O(n)_ | Hard || Sort, BST| 252| [Meeting Rooms](https://leetcode.com/problems/meeting-rooms/) | [C++](./C++/meeting-rooms.cpp) [Python](./Python/meeting-rooms.py) | _O(nlogn)_ | _O(n)_ | Easy |馃摉| | 253| [Meeting Rooms II](https://leetcode.com/problems/meeting-rooms-ii/) | [C++](./C++/meeting-rooms-ii.cpp) [Python](./Python/meeting-rooms-ii.py) | _O(nlogn)_ | _O(n)_ | Medium |馃摉| | 274| [H-Index](https://leetcode.com/problems/h-index/) | [C++](./C++/h-index.cpp) [Python](./Python/h-index.py) | _O(n)_ | _O(n)_ | Medium || Counting Sort | 280| [Wiggle Sort](https://leetcode.com/problems/wiggle-sort/) | [C++](./C++/wiggle-sort.cpp) [Python](./Python/wiggle-sort.py) | _O(n)_ | _O(1)_ | Medium |馃摉| | 324| [Wiggle Sort II](https://leetcode.com/problems/wiggle-sort-ii/) | [C++](./C++/wiggle-sort-ii.cpp) [Python](./Python/wiggle-sort-ii.py) | _O(n)_ on average | _O(1)_ | Medium | variant of [Sort Colors](https://leetcode.com/problems/sort-colors/) | Tri Partition | 347| [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | [C++](./C++/top-k-frequent-elements.cpp) [Python](./Python/top-k-frequent-elements.py) | _O(n)_ on average | _O(n)_ | Medium | | Quick Select, Heap | 406| [Queue Reconstruction by Height](https://leetcode.com/problems/queue-reconstruction-by-height/) | [C++](./C++/queue-reconstruction-by-height.cpp) [Python](./Python/queue-reconstruction-by-height.py) | _O(n * sqrt(n))_ | _O(n)_ | Medium | | | 451| [Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/) | [C++](./C++/sort-characters-by-frequency.cpp) [Python](./Python/sort-characters-by-frequency.py) | _O(n)_ | _O(n)_ | Medium | | | ## Two Pointers | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 19| [Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| [C++](./C++/remove-nth-node-from-end-of-list.cpp) [Python](./Python/remove-nth-node-from-end-of-list.py) | _O(n)_ | _O(1)_ | Easy || 86| [Partition List](https://leetcode.com/problems/partition-list/)| [C++](./C++/partition-list.cpp) [Python](./Python/partition-list.py) | _O(n)_ | _O(1)_ | Medium || 141| [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/)| [C++](./C++/linked-list-cycle.cpp) [Python](./Python/linked-list-cycle.py) | _O(n)_ | _O(1)_ | Easy || 142| [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/)| [C++](./C++/linked-list-cycle-ii.cpp) [Python](./Python/linked-list-cycle-ii.py) | _O(n)_ | _O(1)_ | Medium || 143| [Reorder List](https://leetcode.com/problems/reorder-list/)| [C++](./C++/reorder-list.cpp) [Python](./Python/reorder-list.py) | _O(n)_ | _O(1)_ | Medium || 167| [Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) | [C++](./C++/two-sum-ii-input-array-is-sorted.cpp) [Python](./Python/two-sum-ii-input-array-is-sorted.py) | _O(n)_ | _O(1)_ | Medium | | 259 | [3Sum Smaller](https://leetcode.com/problems/3sum-smaller/) | [C++](./C++/3sum-smaller.cpp) [Python](./Python/3sum-smaller.py) | _O(n^2)_ | _O(1)_ | Medium | 馃摉, LintCode | 283 | [Move Zeroes](https://leetcode.com/problems/move-zeroes/) | [C++](./C++/move-zeroes.cpp) [Python](./Python/move-zeroes.py) | _O(n)_ | _O(1)_ | Easy | | 287| [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)| [C++](./C++/find-the-duplicate-number.cpp) [Python](./Python/find-the-duplicate-number.py) | _O(n)_ | _O(1)_ | Hard | | Binary Search, Two Pointers | 344| [Reverse String](https://leetcode.com/problems/reverse-string/) | [C++](./C++/reverse-string.cpp) [Python](./Python/reverse-string.py) | _O(n)_ | _O(1)_ | Easy | | 345| [Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/) | [C++](./C++/reverse-vowels-of-a-string.cpp) [Python](./Python/reverse-vowels-of-a-string.py) | _O(n)_ | _O(1)_ | Easy | | 349| [Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/) | [C++](./C++/intersection-of-two-arrays.cpp) [Python](./Python/intersection-of-two-arrays.py) | _O(m + n)_ | _O(min(m, n))_ | Easy | EPI | Hash, Binary Search 350| [Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/) | [C++](./C++/intersection-of-two-arrays-ii.cpp) [Python](./Python/intersection-of-two-arrays-ii.py) | _O(m + n)_ | _O(1)_ | Easy | EPI | Hash, Binary Search 360| [Sort Transformed Array](https://leetcode.com/problems/sort-transformed-array/) | [C++](./C++/sort-transformed-array.cpp) [Python](./Python/sort-transformed-array.py) | _O(n)_ | _O(1)_ | Medium |馃摉| 457| [Circular Array Loop](https://leetcode.com/problems/circular-array-loop/) | [C++](./C++/circular-array-loop.cpp) [Python](./Python/circular-array-loop.py) | _O(n)_ | _O(1)_ | Medium || ## Recursion | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 95| [Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/) | [C++](./C++/unique-binary-search-trees-ii.cpp) [Python](./Python/unique-binary-search-trees-ii.py) | _O(4^n / n^(3/2)_ | _O(4^n / n^(3/2)_ | Medium || 98| [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[C++](./C++/validate-binary-search-tree.cpp) [Python](./Python/validate-binary-search-tree.py)| _O(n)_ | _O(1)_ | Medium || 100| [Same Tree](https://leetcode.com/problems/same-tree/) |[C+](./C++/same-tree.cpp) [Python](./Python/same-tree.py) | _O(n)_ | _O(h)_ | Easy || 104| [Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)| [C++](./C++/maximum-depth-of-binary-tree.cpp) [Python](./Python/maximum-depth-of-binary-tree.py)| _O(n)_ | _O(h)_ | Easy || 105| [Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) | [C++](./C++/construct-binary-tree-from-preorder-and-inorder-traversal.cpp) [Python](./Python/construct-binary-tree-from-preorder-and-inorder-traversal.py) | _O(n)_ | _O(n)_ | Medium || 106| [Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) | [C++](./C++/construct-binary-tree-from-inorder-and-postorder-traversal.cpp) [Python](./Python/construct-binary-tree-from-inorder-and-postorder-traversal.py) | _O(n)_ | _O(n)_ | Medium || 108| [Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) | [C++](./C++/convert-sorted-array-to-binary-search-tree.cpp) [Python](./Python/convert-sorted-array-to-binary-search-tree.py) | _O(n)_ | _O(logn)_ | Medium || 109| [Convert Sorted List to Binary Search Tree](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/) | [C++](./C++/convert-sorted-list-to-binary-search-tree.cpp) [Python](./Python/convert-sorted-list-to-binary-search-tree.py) | _O(n)_ | _O(logn)_ | Medium || 110| [Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/) | [Python](./Python/balanced-binary-tree.py) | _O(n)_| _O(h)_ | Easy || 111| [Minimum Depth of Binary Tr

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