274-275. H-Index I & II [Medium]

O(nlogn)
先逆序排序，第i个，引用次数citations[i]，大于等于此citations的文章数i+1，curh是两者的最小，h是所有h的最大

class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        citations.sort(reverse=True)
        h = 0
        for i in range(len(citations)):
            curh = min(citations[i], i+1)
            h = max(h, curh)
        return h

O(n)，用一个数组长(n+1)，记录引用次数，从后往前，当前引用是i，大于等于此引用次数的文章数是curCit，返回最小的那个

class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        temp = [0] * (len(citations) + 1)
        for i in citations:
            if i > len(citations):
                temp[-1] += 1
            else:
                temp[i] += 1
        curCit = 0
        for i in range(len(citations),-1,-1):
            curCit += temp[i]
            if curCit >= i:
                return i
        return 0

275和274一模一样，只不过给了排好序的。