LeetCode – H-Index (Java)

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. 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.

Java Solution 1

public int hIndex(int[] citations) {
    int result = 0;
    for(int i=citations.length-1; i>=0; i--){
        int cnt = citations.length-i;
            result = cnt;
    return result;

Java Solution 2

We can also put the citations in a counting sort array, then iterate over the counter array.

public int hIndex(int[] citations) {
    int len = citations.length;
    int[] counter = new int[len+1];
    for(int c: citations){
    int k=len;
    for(int s=counter[len]; k > s; s += counter[k]){
    return k;
Category >> Algorithms  
If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:
String foo = "bar";
  • James Alikhani

    My solution in Python3:

    def get_H_index(citations):
    n = len(citations)
    h_index = 0
    for i in range(n):
    if citations[i]>i:
    h_index += 1
    return h_index