# Program to find H-Index from a list of citations in C++

Suppose we have an array of citations of a researcher. We have to define a function to compute the researcher's h-index. As we know the h-index is a metric used to calculate the impact of a researcher's papers. Formally H-index can be defined as: "A researcher has index h if h of their 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 = [5, 4, 1, 2, 6], then the output will be 3, as at least 3 papers have at least 3 citations each − 4, 5, 6.

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

Let us see the following implementation to get better understanding −

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int solve(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 = {5, 4, 1, 2, 6};
cout << (ob.solve(v));
}

## Input

[5, 4, 1, 2, 6]

## Output

3

Updated on: 19-Nov-2020

234 Views