leetcode 274: H-Index

H-Index

Total Accepted: 2684 Total Submissions: 11955

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.

[思路]

counting sort 的变种.

[CODE]

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