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Question

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.

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

Hint:

1. An easy approach is to sort the array first.
2. What are the possible values of h-index?
3. A faster approach is to use extra space.

Solution

Result: Accepted Time: 4 ms

Here should be some explanations.

class Solution {
public:
    int hIndex(vector<int>& cit) {
        if(cit.size() < 1) return 0;
        sort(cit.begin(),cit.end());
        reverse(cit.begin(),cit.end());
        int i;
        for( i = 0; i < cit.size() && cit[i] > i; i++);
        return i;
    }
};

Complexity Analytics

• Time Complexity: $O(nlog(n))$
• Space Complexity: $O(1)$