leetcode 34在排序数组中查找元素的第一个和最后一个位置

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        vector<int> res(,-);
        int left=;int right=nums.size()-;
        if(right<) return res;
        if(right==){
            if(nums[]==target) return{,};
            else return res;
        }
        int mid;
        //寻找lower_bound
        while(left<right){
            int mid=left+(right-left)/;
            if(nums[mid]<target)
                left=mid+;
            else
                right=mid;
        }
        if(nums[left]==target){
            res[]=left;
            int step=;
            while(step+left<nums.size()&&nums[step+left]==target)
                step++;
            res[]=left+step-;
        }
        return res;
    }
};