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：
1 class Solution { 2 public: 3 int hIndex(vector<int>& citations) { 4 int n = citations.size(); 5 vector<int>index(n + 1, 0);//注意这里是n+1 6 for(int i = 0; i < n; ++i){ 7 if(citations[i]>=n) 8 index[n]++; 9 else 10 index[citations[i]]++; 11 } 12 if(index[n] >= n) return n; 13 for(int i = citations.size()-1; i >= 0; --i){ 14 index[i]+=index[i+1]; 15 if(index[i] >= i) 16 return i; 17 } 18 return 0; 19 } 20 };