原题的中文翻译不是很好，所以给出英文版。
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."
Example:
Input: citations = [3,0,6,1,5] Output: 3 Explanation: [3,0,6,1,5] 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, her h-index is 3.
Note: If there are several possible values for h, the maximum one is taken as the h-index.
我的理解：
h指数就是在总N篇文章中有h篇文章中引用次数至少为h。
剩下的N-h篇文章的引用次数不超过h。
找最大的h，最大的h为N，所以从h = N开始遍历验证。
class Solution {
public:
int hIndex(vector<int>& citations)
{
sort(citations.begin(), citations.end());
int ans = citations.size();
for (int i = 0; i < citations.size(); i++)
{
if (ans <= citations[i])
{
break;
}
//文章数-1, h指数-1
else
{
ans--;
}
}
return ans;
}
};