public class HIndexII { public static int hIndex(int[] citations) { if (citations== null || citations.length == 0) { return 0; } final int N = citations.length; int start = 0, end = N - 1; while (start + 1 < end) { int mid = start + (end - start) / 2; // at least h cite h paper if (citations[mid] > N - mid) { end = mid; } else if (citations[mid] < N - mid) { start = mid; } else { return N - mid; } } if (citations[start] >= N - start) { return N - start; } if (citations[end] >= N - end) { return N - end; } return 0; } }