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

题意：计算H索引。

思路：直接按定义计算。

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