LeetCode之Search for a Range

/*这道题本质上是考二分搜索。解题思路为：
1.先用二分搜索找到数组中需要查找数字的下标；
2.从给下标向左右扩展，获取它最左最右的下标并返回结果。*/
class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int left, right, idx;
        idx = binarySearch(nums, target);
        if(idx == -1){
            left = -1;
            right = -1;
        }
        else{
            int i = idx;;
            while(i >= 0 && nums[i] == target) --i;
            left = i+1;
            while(idx < nums.size() && nums[idx] == target) ++idx;
            right = idx-1;
        }
        vector<int> res;
        res.push_back(left);
        res.push_back(right);
        return res;
    }
    
    int binarySearch(const vector<int> &nums, int target){
        int left(0), right(nums.size()-1);
        while(left <= right){
            int mid = (left + right) / 2;
            if(nums[mid] == target) return mid;
            else if(nums[mid] < target) left = mid+1;
            else right = mid-1;
        }
        return -1;
    }
};