[LeetCode] 274. H-Index Java

题目：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.

代码：

public class Solution {
    public int hIndex(int[] citations) {
        int n = citations.length, tot=0;
        int[] arr = new int[n+1];
        for (int i=0; i<n; i++) {
            if (citations[i]>=n) arr[n]++;
            else arr[citations[i]]++;
        }
        for (int i=n; i>=0; i--) {
            tot += arr[i];
            if (tot>=i) return i;
        }
        return 0;
    }
}