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LeetCode 34 在排序数组中查找元素的第一个和最后一个位置 (C语言 二分查找法)

宁静的猫 2022-01-08 阅读 80

题目:

进阶:

示例1:

示例2:

示例3:

提示:

解题代码:

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */

int binarySearch(int* nums, int left, int right, int target){
    if(left > right)
        return -1;
    int mid = (left + right) / 2;
    if(nums[mid] == target)
        return mid;
    else if(nums[mid] > target)
        return binarySearch(nums, left, mid - 1, target);
    else
        return binarySearch(nums, mid + 1, right ,target);
        
    return -1;
}

int* searchRange(int* nums, int numsSize, int target, int* returnSize){
    *returnSize = 2;
    int* retNums = (int*)malloc(2 * sizeof(int));
    retNums[0] = -1;
    retNums[1] = -1;
    // 二分查找法找到target在数组中的位置
    int index = binarySearch(nums, 0, numsSize - 1, target);
    if(index == -1)
        return retNums;
    // 找到左边界
    if(index > 0)
        while(index > 0 && nums[index] == nums[index-1])
            index--;
    retNums[0] = index;
    // 找到右边界
    if(index < numsSize - 1)
        while(index < numsSize - 1 && nums[index] == nums[index+1])
            index++;
    retNums[1] = index;
    return retNums;
}

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