import java.util.Arrays; public class HIndex { public static int hIndex_sort(int[] citations) { if (citations == null || citations.length == 0) { return 0; } Arrays.sort(citations); final int N = citations.length; for (int i = 0; i < N; i++) { if (citations[i] >= N - i) { return N - i; } } return 0; } public int hIndex_count(int[] citations) { if (citations == null || citations.length == 0) { return 0; } final int N = citations.length; int[] papers = new int[N + 1]; for (int c: citations) { papers[Math.min(N, c)]++; } int h = N; // citation // find first h that, h paper has at least h citations for (int count = papers[N]; count < h; count += papers[h]) { h--; } return h; } }