H-Index II

c++

class Solution {public:    int hIndex(vector<int>& citations) {        if (citations.empty()) return 0;        //sort(citations.begin(), citations.end());        int n = citations.size();        int st = 0;         int ed = n - 1;        int res = 0;        while (st <= ed) {            int mid = (st + ed) / 2;            if (citations[mid] >= n - mid) {                res = n - mid;                ed = mid - 1;            }            else {                st = mid + 1;            }        }        return res;    }};