二分法确定左右边界

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        if(nums.size()==0)
            return {-1, -1};
        int l = 0, r = nums.size() - 1;
        while (l < r)
        {
            int mid = (l + r) >> 1;
            if (nums[mid] < target)
                l = mid + 1;
            else
                r = mid;
        }
        if(nums[l]!=target)
            return {-1, -1};
        int begin = l;
        l = 0, r = nums.size() - 1;
        while (l <= r)
        {
            int mid = (l + r) >> 1;
            if (target < nums[mid])
                r = mid - 1;
            else 
                l = mid + 1;
        }
        int end = r;
        return {begin,end};

        
    }
};