274

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n=citations.size();
        vector<int> h(n+1, 0);
        for(auto c: citations)
            h[min(n,c)]++;
        int ans=n;
        for(int sum=h[n]; sum<ans; sum+=h[ans])
            ans--;
        return ans;
    }
};