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, 5citations 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.

来源： https://leetcode.com/problems/h-index/

分析

需要看懂 H-index 的定义

   如果作者有 X 篇文章的引用，每个都不少于 X，那么其 H-index 是 X

可以看出，最大 H-index 是文章总数

所以建立一个长度为 citations.size() + 1 的数组A，A[i] 代表引用次数大于 i 的文章数。

遍历一遍引用数据，然后从数组 A 的尾部向前查找，直到发现 总数 大于 i，即为所求

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class Solution { public:     int hIndex(vector<int>& citations) {         sort(citations.begin(), citations.end());         int len = citations.size();         vector<int> A(len + 1, 0);         int h_count = 0, h_index = 0;                  for(int i = 0; i < len; ++i){             citations[i] >= len ? ++A[len]: ++A[citations[i]];         }                   for(int i = len; i >=0; --i){             h_count += A[i];             if(h_count >= i){                 h_index = i;                 break;             }         }         return h_index;     } };

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