274. 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.

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

代码（python实现）

class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        hIndex = 0
        
        if citations is None or len(citations) == 0:
            return 0
            
        if len(citations) == 1:
            if citations[0] == 0:
                return 0
            else:
                return 1
    
            
        citations.sort()
        
        q = len(citations) - 1
        count = 1
        
        if citations[0] >= len(citations):
            return len(citations)
        
        while(q >= 0):
            if citations[q] < count or citations[q] == 0:
                break
            #从右往左扫描，如果count在citations[q - 1]和citations[q]之间，则hIndex = count
            if count >= citations[q - 1] and count <= citations[q]:
                hIndex = count
            count += 1    
            q -= 1
               
        return hIndex