Formatted question description:

 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."


 Input: citations = [3,0,6,1,5]
 Output: 3

 Explanation: [3,0,6,1,5] 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, her h-index is 3.

 Note: If there are several possible values for h, the maximum one is taken as the h-index.


  1. Sort all SCI papers published by him in descending order of the number of citations;
  2. Search the sorted list from front to back until the serial number of a paper is greater than the number of times the paper has been cited.

The obtained serial number minus one is the H index



public class H_Index {
    class Solution {
        public int hIndex(int[] citations) {

            if (citations == null || citations.length == 0) {
                return 0;

            // @note
            Arrays.sort(citations); // 6,5,3,1,0
            for (int i = 0; i < citations.length / 2; ++i) {
                int temp = citations[i];
                citations[i] = citations[citations.length - i - 1];
                citations[citations.length - i - 1] = temp;

            for (int i = 0; i < citations.length; ++i) {
                if (citations[i] <= i) { // @note: <i then return i+1 will not work
                    return i;

            return citations.length;


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