暑假刷题训练营打卡7.31

[@心海]

第一题

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        if (head == null || head.next == null) {
            return true;
        }
        ListNode slow = head, fast = head, pre = head;
        while (fast != null && fast.next != null) {
            pre = slow;
            slow = slow.next;
            fast = fast.next.next;
        }
        ListNode next = slow.next;
        slow.next = null;
        while (next != null) {
            pre = slow;
            slow = next;
            next = next.next;
            slow.next = pre;
        }
        ListNode newHead = slow;
        while (head != null && newHead != null) {
            if (head.val != newHead.val) {
                return false;
            }
            newHead = newHead.next;
            head = head.next;
        }
        return true;  
    }
}

第二题

class Solution {
    public List<List<String>> partition(String s) {
        int n = s.length();
        boolean[][] dp = new boolean[n + 2][n + 2];
        int[] tmp = new int[(n + 2) * (n + 2)];
        int cnt = 0;
        List<List<String>> ans = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j <= i; j++) {
                if (i == j) {
                    dp[i][j] = true;
                } else {
                    if (s.charAt(i) == s.charAt(j)) {
                        if (i==j+1){
                            dp[i][j] = true;
                        }else {
                            dp[i][j] = dp[i - 1][j + 1];
                        }
                    } else {
                        dp[i][j] = false;
                    }
                }
                if (dp[i][j]) {
                    tmp[cnt] = i * 100 + j;
                    cnt++;
                }
            }
        }
        List<Set<String>> x = new ArrayList<>();
        x.add(new HashSet<>());
        x.get(0).add(s.charAt(0) + "#" + 0);
        for (int i = 1; i < cnt; i++) {
            int l = tmp[i] % 100;
            int r = tmp[i] / 100;
            Set<String> iSet = new HashSet<>();
            x.add(iSet);
            String tmpS = s.substring(l, r + 1);
            for (int j = 0; j < i; j++) {
                Set<String> y = x.get(j);
                if (l == 0) {
                    iSet.add(tmpS + "#" + r);
                }else {
                    for (String z : y) {
                        int hasr = Integer.parseInt(z.split("#")[1]);
                        if (l == hasr + 1) {
                            iSet.add(z.replace("#" + hasr, "") + "," + tmpS + "#" + r);
                        }
                    }
                }
            }
        }
        for (int i = 0; i < cnt; i++) {
            Set<String> y = x.get(i);
            for (String z : y) {
                if (Integer.parseInt(z.split("#")[1]) == n - 1) {
                    String[] xx = z.replace("#" + (n - 1), "").split(",");
                    List<String> yy = new ArrayList<>();
                    for (int j = 0; j < xx.length; j++) {
                        yy.add(xx[j]);
                    }
                    ans.add(yy);
                }
            }
        }
        return ans;
    }
}

 

第三题

class Solution {
    public int primePalindrome(int n) {
        while (true) {
            if (n == reverse(n) && isPrime(n))
                return n;
            n++;
            if (10_000_000 < n && n < 100_000_000)
                n = 100_000_000;
        }
    }
    public boolean isPrime(int n) {
        if (n < 2) return false;
        int R = (int) Math.sqrt(n);
        for (int d = 2; d <= R; ++d)
            if (n % d == 0) return false;
        return true;
    }
    public int reverse(int n) {
        int ans = 0;
        while (n > 0) {
            ans = 10 * ans + (n % 10);
            n /= 10;
        }
        return ans;
    }
}

 

第四题