Leetcode 274: H-Index

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.Length == 0) return 0;
        
        var h = new int[citations.Length + 1];
        
        for (int i = 0; i < citations.Length; i++)
        {
            if (citations[i] >= citations.Length)
            {
                h[citations.Length]++;
            }
            else
            {
                h[citations[i]]++;
            }
        }
        
        int c = 0;
        for (int i = citations.Length; i >=0; i--)
        {
            c += h[i];
            
            if (c >= i)
            {
                return i;
            }
        }
        
        return 0;
    }
}