34. Find First and Last Position of Element in Sorted Array

最新推荐文章于 2022-07-27 22:53:20 发布

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最新推荐文章于 2022-07-27 22:53:20 发布

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博客给出一个升序排列的整数数组，要求找出给定目标值在数组中的起始和结束位置，算法时间复杂度需为O(log n)，若未找到目标值则返回[-1, -1]，并给出了两个示例。

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题目链接
Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm’s runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

vector<int> searchRange(vector<int>& nums, int target) {
        if(nums.empty()) return vector <int> ({-1,-1});
        int l,r;
        vector <int> res;
        l = 0,r = nums.size() - 1;
        while(l < r){ //寻找大于等于target的最左边的值
            int mid = l + r >> 1;
            if(nums[mid] >= target) r = mid;
            else l = mid + 1;
        }
        if(nums[l] != target) return vector <int> ({-1,-1});
        res.push_back(l);
        l = 0,r = nums.size() - 1;
        while(l < r){//寻找大于等于target的最右边的值
            int mid = l + r + 1 >> 1;
            if(nums[mid] <= target) l = mid;
            else r = mid - 1;
        }
        res.push_back(r);
        return res;
}