Leetcode187: 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.

Hint:

1. An easy approach is to sort the array first.
2. What are the possible values of h-index?
3. A faster approach is to use extra space.

H-Index的核心计算方法如下：

             1、将某作者的所有文章的引用频次按照从大到小的位置排列

             2、从前到后，找到最后一个满足条件的位置，其条件为：

                           此位置是数组的第x个，其值为y，必须满足 y >= x;

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