LeetCode 274. H-Index

Problem:　　https://leetcode.com/problems/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."

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.

 

Thought:

have an extra space to note bucket[i] papers have i citation, when n, bucket[n] = times more than n

Reference: https://leetcode.com/discuss/93819/java-bucket-sort-o-n-solution-with-detail-explanation

 

Code C++:

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size();
        int* bucket = new int[n+1];
        for (int i = 0; i <= n; i++){
            bucket[i] = 0;
        }
        
        for (int i = 0; i < citations.size(); i++) {
            if (citations[i] > n) {
                bucket[n]++;
            } else {
                bucket[citations[i]]++;
            }
        }
        
        int count = 0;
        for (int i = n; n >= 0; i--) {
            count += bucket[i];
            if (count >= i) {
                return i;
            }
        }
        return 0;
    }
};