int hIndex(vector<int>& citations) {

if(citations.empty()) return 0;

int n = citations.size();

int hIndx = 0;

int left = 0, right = n - 1;

while(left <= right) {

if(left == right) {

return min(citations[left], n - left);

}

int mid = left + (right - left) / 2;

if(citations[mid] < n - mid) {

left = mid + 1;

} else {

hIndx = n - mid;

right = mid;

}

}

return hIndx;

}