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

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.

Runtime: 4 ms, faster than 72.66% of C++ online submissions for H-Index.

STL的應用。

#define ALL(x) (x).begin(),(x).end()
#include <vector>
#include <algorithm>
using namespace std;
class Solution {
public:
  int hIndex(vector<int>& citations) {
    sort(ALL(citations));
    reverse(ALL(citations));
    int idx = citations.size()+1;
    for(int i=0; i<citations.size(); i++){
      if(citations[i] < i+1) {
        idx = i+1;
        break;
      }
    }
    return idx-1;
  }
};