两次二分查找，第一次找low，第二次找high
[l,r)找high和(l,r]找low

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