H-Index in C++

Suppose we have an array of citations (The citations are non-negative integers) of a researcher. We have to define a function to compute the researcher's h-index. According to the definition of h-index: "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."

So if the input is like citations = [3,0,6,1,7], then the output will be 3, as it indicates that the researcher has five papers, they have got 3, 0, 6, 1, 7 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two paper with no more than 3 citations each, then the h-index is 3.

To solve this, we will follow these steps −

• n := size of the array, create one array called bucket of size n + 1

• for i in range 0 to n – 1

  • x := c[i]

  • if x >= n, then increase bucket[n] by 1, otherwise increase bucket[x] by 1

• cnt := 0

• for i in range n down to 0 −

  • increase cnt by bucket[i]

  • if cnt >= i, then return i

• return – 1

Example(C++)

Let us see the following implementation to get a better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
   public:
   int hIndex(vector<int>& c) {
      int n = c.size();
      vector <int> bucket(n + 1);
      for(int i = 0; i < n; i++){
         int x = c[i];
         if(x >= n){
            bucket[n]++;
         } else {
            bucket[x]++;
         }
      }
      int cnt = 0;
      for(int i = n; i >= 0; i--){
         cnt += bucket[i];
         if(cnt >= i)return i;
      }
      return -1;
   }
};
main(){
   Solution ob;
   vector<int> v = {3,0,6,1,7};
   cout << (ob.hIndex(v));
}

Input

[3,0,6,1,7]

Output

3