class Solution {public:    int hIndex(vector
     
      & citations) {        if (citations.size() == 0)  return 0;        int i = 0, j = citations.size();        while (i < j - 1) {            int m = i + (j - i) / 2;            int pos = citations.size() - m;            if (m == citations[pos])                return m;            else if (m > citations[pos])                j = m;            else                i = m;        }        if (j == citations.size() && citations[0] >= citations.size() ||             citations[citations.size() - j] >= j)            return j;        return i;    }};