Sum of all minimum frequency elements in Matrix

Given a NxM matrix of integers containing duplicate elements. The task is to find the sum of all minimum occurring elements in the given matrix. That is the sum of all such elements whose frequency is even in the matrix.

Examples:

Input : mat[] = {{1, 1, 2},
                {2, 3, 3},
                {4, 5, 3}}
Output : 9
The min occurring elements are 4, 5 and they 
occurs only 1 time.
Therefore, sum = 4+5 = 9

Input : mat[] = {{10, 20},
                 {40, 40}}
Output : 30


Approach:

  • Traverse the matrix and use a map in C++ to store the frequency of elements of the matrix such that the key of map is the matrix element and value is its frequency in the matrix.
  • Then traverse the map to find the minimum frequency.
  • Finally, traverse the map to find the frequency of elements and check if it matches with the minimum frequency obtained in previous step, if yes, then add this element it’s frequency times to sum.

Below is the implementation of the above approach:

C++

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// C++ program to find sum of all min
// frequency elements in a Matrix
  
#include <bits/stdc++.h>
using namespace std;
  
#define N 3 // Rows
#define M 3 // Columns
  
// Function to find sum of all min
// frequency elements in a Matrix
int sumMinOccurring(int arr[N][M])
{
    // Store frequencies of elements
    // in matrix
    map<int, int> mp;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            mp[arr[i][j]]++;
        }
    }
  
    // Find minimum frequency
    int sum = 0;
    int minFreq = INT_MAX;
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        if (itr->second < minFreq)
            minFreq = itr->second;
    }
  
    // Sum of minimum frequency elements
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        if (itr->second == minFreq) {
            sum += (itr->first) * (itr->second);
        }
    }
  
    return sum;
}
  
// Driver Code
int main()
{
  
    int mat[N][M] = { { 1, 2, 3 },
                      { 1, 3, 2 },
                      { 1, 5, 6 } };
  
    cout << sumMinOccurring(mat) << endl;
  
    return 0;
}

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Python3

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# Python3 program to find sum of all min 
# frequency elements in a Matrix 
  
import sys
import math
  
# Store frequencies of elements 
# in matrix
def sumMinOccuring(mat):
    n,m=len(mat),len(mat[0])
    _map={}
    for i in range(n):
        for j in range(m):
            d=mat[i][j]
            if d in _map:
                _map[d]=_map.get(d)+1
            else:
                _map[d]=1
  
    # Find minimum frequency
    _sum,minFreq=0,sys.maxsize
    for i in _map:
        minFreq=min(minFreq,_map.get(i))
      
    # Sum of minimum frequency elements
    for i in range(n):
        for j in range(m):
            if _map.get(mat[i][j])==minFreq:
                _sum+=mat[i][j]
      
    return _sum
   
# Driver Code
if __name__=='__main__':
    mat=[[1,2,3],[1,3,2],[1,5,6]]
    print(sumMinOccuring(mat))
  
  
# This code is Contributed by Vikash Kumar 37

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Output:

11

Time Complexity : O(M x N)
Auxiliary Space : O(M x N)



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Improved By : Vikash Kumar 37