Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index. According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each.” For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, his h-index is 3. Note: If there are several possible values for h, the maximum one is taken as the h-index.

public class Solution {
    public int hIndex(int[] citations) {
        if (citations == null || citations.length == 0) return 0;
        Arrays.sort(citations);
        int len = citations.length;
        for (int i = 0; i < citations.length; i++) {
            if (len <= citations[i]) {
                break;
            } else {
                len--;
            }
        }
        return len;
    }
}

class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        if not citations:
            return 0

        citations.sort()
        hindex = len(citations)
        for citation in citations:
            if citation >= hindex:
                break
            else:
                hindex -= 1
        return hindex