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

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

An easy approach is to sort the array first.

Solution

• Sort + Binary Search

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class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        if citations == None or len(citations) == 0:
            return 0

        citations = sorted(citations)
        start = 0
        end = len(citations)-1

        while start <= end:
            mid = (start+end)/2
            if citations[mid] < len(citations)-mid:
                start = mid+1
            else:
                end = mid-1
        return len(citations)-start