Leetcode 274. H-Index

Description: Given an array of integers citations where citations[i] is the number of citations a researcher received for their i^th paper, return compute the researcher's h-index.

According to the definition of h-index on Wikipedia: A scientist has an index h if h of their n papers have at least h citations each, and the other n − h papers have no more than h citations each. If there are several possible values for h, the maximum one is taken as the h-index.

Link: 274. H-Index

Examples:

Example 1:
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, their h-index is 3.

Example 2:
Input: citations = [1,3,1]
Output: 1

思路: n中有h个大于等于h的数，有n-h个不大于h 的数，找到满足以上条件的最大的h。首先升序排序，如果采用逐个遍历太慢了，所以可以binary search.

class Solution(object):
    def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        # there is h numbers in the list that are equal or more than h
        # sort and binary search
        citations.sort()
        N = len(citations)
        l = 0
        r = N - 1
        res = 0
        while l <= r:
            mid = l + (r-l) / 2   # index 
            res = max(res, min(citations[mid], N-mid))
            if citations[mid] < N - mid:
                l = mid + 1
            else:
                r = mid - 1
        return res

手动过一遍就能理解 max(res, min(citations[mid], N-mid))。

日期: 2021-03-31 为什么总是不快乐