LeetCode OJ：H-Index（H指数）

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.

感觉这题更加像动归，没写出来，看了别人的实现，代码如下：

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size();
        vector<int>index(n + 1, 0);//注意这里是n+1
        for(int i = 0; i < n; ++i){
            if(citations[i]>=n)
                index[n]++;
            else
                index[citations[i]]++;
        }
        if(index[n] >= n) return n;
        for(int i = citations.size()-1; i >= 0; --i){
            index[i]+=index[i+1];
            if(index[i] >= i)
                return i;
        }
        return 0;
    }
};