二分查找

int binary_search(int[] nums, int target) {  
    int left = 0, right = nums.length - 1;  
    while (left <= right) {  
    int mid = left + (right - left) / 2;  
    if (nums[mid] < target) {  
        left = mid + 1;  
    } else if (nums[mid] > target) {  
        right = mid - 1;  
    } else if (nums[mid] == target) {  
        // 别返回，锁定左侧边界  
        right = mid - 1;  
        // 别返回，锁定右侧边界  
        //left = mid + 1;  
    }  
    }  
    // 最后要检查 left 越界的情况  
    if (left >= nums.length || nums[left] != target)  
    return -1;  
    return left;  
    // 最后要检查 right 越界的情况  
    //if (right < 0 || nums[right] != target)  
    //    return -1;  
    //return right;  
}