Array elements that appear multiple times?

Here we will see a problem. We have an array. Our task is to find those elements whose frequency is greater than 1. Suppose the elements are {1, 5, 2, 5, 3, 1, 5, 2, 7}. Here 1 appears 2 times, 5 appears 3 times, 2 appears 3 times, and the others only appear once. So the output will be {1, 5, 2}

Algorithm

moreFreq(arr, n)

Begin
   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 is more than 1, then print the key
End

Example

#include <iostream>
#include <map>
using namespace std;
void moreFreq(int arr[], int n){
   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 (it->second > 1)
         cout << it->first << " ";
   }
}
int main() {
   int arr[] = {1, 5, 2, 5, 3, 1, 5, 2, 7};
   int n = sizeof(arr)/sizeof(arr[0]);
   cout << "Frequency more than one: ";
   moreFreq(arr, n);
}

Output

Frequency more than one: 1 2 5

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