274. H-Index

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LeetCode

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Problem

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.”

Example:

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.

Code

class Solution {
    public int hIndex(int[] citations) {
        if(citations == null || citations.length == 0) return 0;
        
        Arrays.sort(citations);
        
        int count = 1;
        
        for(int i = citations.length - 1; i >= 0; i--){
            if(count <= citations[i]){
                count++;
            } else {
                return count - 1;
            }
        }
        
        return count - 1;
    }
}

class Solution:
    def hIndex(self, citations: List[int]) -> int:
        citations.sort(reverse=True)

        res = 0
        for i in range(len(citations)):
            if i + 1 <= citations[i]:
                res = i + 1

        return res