LeetCode 34. 在排序数组中查找元素的第一个和最后一个位置

给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。

你的算法时间复杂度必须是 O(log n) 级别。

如果数组中不存在目标值，返回 [-1, -1]。

示例 1:

输入: nums = [5,7,7,8,8,10], target = 8
输出: [3,4]
示例 2:

输入: nums = [5,7,7,8,8,10], target = 6
输出: [-1,-1]

 

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        if (nums.empty())
            return {-1, -1};
        
        int left = left_bound(nums, target);
        if (left == -1)
            return {-1, -1};
        else
            return {left, right_bound(nums, target)};
    }

    int left_bound(vector<int>& nums, int target) {
        int low = 0, high = nums.size() - 1, mid;
        while (low <= high)
        {
            mid = (low + high) / 2;
            if (nums[mid] >= target)
                high = mid - 1;
            else
                low = mid + 1;
        }
        if (low >= nums.size() || nums[low] != target)
            return -1;
        return low;
    }

    int right_bound(vector<int>& nums, int target) {
        int low = 0, high = nums.size() - 1, mid;
        while (low <= high)
        {
            mid = (low + high) / 2;
            if (nums[mid] > target)
                high = mid - 1;
            else
                low = mid + 1;
        }
        if (high < 0 || nums[high] != target)
            return -1;
        return high;
    }
};