【算法专题三】查找/排序算法

// 标准二分法
int BinarySearch (vector nums, int target) 
{
    if (nums.empty()) {
        return -1;
    }
    int left = 0;
    int right = nums.size() - 1;
    
    while (left <= right) {
        int mid = (right - left) / 2 + left;
        if (nums[mid] == target) {
            return mid;
        } else if (nums[mid] > target) {
            right = mid - 1;
        } else if (nums[mid] < target) {
            left = mid + 1;
        }
    }
    return -1; 
}



// 搜索左边界
int left_bound(int[] nums, int target)
{
    if (nums.length == 0)
        return -1;
    int left = 0;
    int right = nums.length; // 注意
    while (left < right) { // 注意
        int mid = (left + right) / 2;
        if (nums[mid] == target) {
            right = mid;
        }
        else if (nums[mid] < target) {
            left = mid + 1;
        }
        else if (nums[mid] > target) {
            right = mid; // 注意
        }
    }
    return left;
}