Array elements with prime frequencies?

Suppose we have one array. we have to count how many of the elements present in the array prime number of times. So if the array is {1, 2, 2, 0, 1, 5, 2, 5, 0, 0, 1, 1}, then 1 is present 4 times, 2 is present 3 times, 0 is present 3 times, and 5 is present 2 times. So there are three elements {2, 0, 5} that have occurred prime number of times. So the count will be 3.

Algorithm

countPrimeOccurrence(arr, n)

Begin
   count := 0
   define map with int type key and int type value
   for each element e in arr, do
      increase map.key(arr).value
   done
   for each key check whether the value corresponding the value is prime or not, if prime, then increase count.
   return count
End

Example

#include <iostream>
#include <map>
using namespace std;
bool isPrime(int n){
   for(int i = 2; i<=n/2; i++){
      if(n % i == 0){
         return false;
      }
   }
   return true;
}
int countPrimeOcurrence(int arr[], int n){
   int count = 0;
   map<int, int> freq_map;
   for(int i = 0; i<n; i++){
      freq_map[arr[i]]++; //increase the frequency
   }
   for (auto it = freq_map.begin(); it != freq_map.end(); it++) {
      if (isPrime(it->second))
         count++;
   }
   return count;
}
int main() {
   int arr[] = {1, 2, 2, 0, 1, 5, 2, 5, 0, 0, 1, 1};
   int n = sizeof(arr)/sizeof(arr[0]);
   cout << "Prime frequency count: " << countPrimeOcurrence(arr, n);
}

Output

Prime frequency count: 3

Arnab Chakraborty

Updated on 02-Jul-2020 09:45:57

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