[学习报告]《LeetCode零基础指南》(第四讲) 指针

[星星之火]

一、今日知识点总结

1.指针的使用

2.字符串结尾为'\0'

3.判断奇偶还可以用if(x&1)

二、今日做题记录

三、解题报告

1108. IP 地址无效化

char * defangIPaddr(char * address){
    char *ret = (char *)malloc(1000 * sizeof(char));   // (1)
    int returnSize = 0;
    int i;
    for(i = 0; address[i]; ++i) {                      // (2)
        if(address[i] == '.') {
            ret[ returnSize++ ] = '[';
            ret[ returnSize++ ] = '.';
            ret[ returnSize++ ] = ']';
        }else {
            ret[ returnSize++ ] = address[i];
        }
    }
    ret[ returnSize ] = '\0';                          // (3)
    return ret;
}

剑指 Offer 58 - II. 左旋转字符串

char* reverseLeftWords(char* s, int n){
    int i;
    int k=strlen(s);
    char *ret=(char *)malloc((k+1)*sizeof(char));
    for(i=0;i<=k-n-1;++i){
        ret[i]=s[i+n];
    }
    for(i=0;i<=n-1;i++){
        ret[k-n+i]=s[i];
    }
    ret[k]='\0';
    return ret;
}

1480. 一维数组的动态和

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* runningSum(int* nums, int numsSize, int* returnSize){
    int *ret=(int *)malloc(sizeof(int)*numsSize);int i,j,sum;
    for(i=0;i<=numsSize-1;++i){
        sum=0;
        for(j=0;j<=i;++j){
            sum+=nums[j];
        }
        ret[i]=sum;
    }
    *returnSize=numsSize;
    return ret;
}

1920. 基于排列构建数组

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* buildArray(int* nums, int numsSize, int* returnSize){
    int *ret=(int *)malloc(sizeof(int)*numsSize);int i;
    for(i=0;i<=numsSize-1;++i){
        ret[i]=nums[nums[i]];
    }
    *returnSize=numsSize;
    return ret;
}

1929. 数组串联

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* getConcatenation(int* nums, int numsSize, int* returnSize){
    int *ret=(int *)malloc(2*sizeof(int)*numsSize);int i;
    for(i=0;i<=numsSize-1;++i){
        ret[i+numsSize]=ret[i]=nums[i];
    }
    *returnSize=2*numsSize;
    return ret;
}

1470. 重新排列数组

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* shuffle(int* nums, int numsSize, int n, int* returnSize){
    int *ret=(int *)malloc(sizeof(int)*numsSize);int i;
    for(i=0;i<=numsSize-1;++i){
        if(i&1){//判断i是否为奇数
            ret[i]=nums[n+i/2];//是奇数取y值
        }else{
            ret[i]=nums[i/2];
        }
    }
    *returnSize=numsSize;
    return ret;
}

四、总结

 

/**
 * Note: The returned array must be malloced, assume caller calls free().  // (1)
 */
 int *func(int *nums, int numsSize, int *returnSize) {                     // (2)
     int *ret = (int *)malloc( sizeof(int) * xxx );                        // (3)
     // TODO                                                               // (4)
     *returnSize = xxx;                                                    // (5)
     return ret;                                                           // (6)
 }