LeetCode 274

class Solution {
public:
    int hIndex(vector<int>& citations) {
        if (citations.size() == 0) return 0;
        int num = citations.size();
        sort(citations.begin(), citations.end());
        for (int i = 0; i < citations.size(); i++) {
            if (citations[i]>=num) {
                return num;
            } else {
                num--;
            }
        }
        return 0;
    }
};