Count all pairs of rows and columns which are equal

Last Updated : 23 Jul, 2025

Given a matrix mat[][] of size N * N (1 ? N ? 1000), the task is to find the number of pairs of rows and columns (Rowi, Colj), such that row Rowi and column Colj are equal.

Note: A row and column pair are considered equal if they contain the same elements in the same order (i.e. an equal array).

Example:

Input: 

Matrix
Matrix

Output: 3
Explanation: The row-column pairs are {1, 1}, {3, 2}, {3, 3}.

Input: 

Example matrix
Example matrix

Output: 6

An approach using Hashing:

Iterate on the matrix and keep all the elements of each row into a string and store these strings into map with their frequency. Iterate over the map and keep all the elements of each column into a string and then check if column string has any occurrence into map. If there exist any occurrence into map then keep adding their count into result.

Follow the steps below to implement the above idea:

  • Initialize a map for mapping all columns with their frequency of occurrence.
  • Iterate over every row
    • Initialize an empty string s = "".
    • Keep appending all the elements into the string s.
    • Increment the frequency count of string s in the map
    • Initialize a result variable for storing the number of pairs such that the row and column are equal
  • Iterate over every column
    • Initialize an empty string s = "".
    • Keep appending all the elements into the string s.
    • Add into the result of the frequency count of s in the map.
  • Return the result.

Below is the implementation of the above approach.

C++ 
// C++ code to implement the approach

#include <bits/stdc++.h>
using namespace std;

// Function to count the row-column pairs
int equalPairs(vector<vector<int> >& grid)
{
    // Initialize a map for mapping all
    // column with their frequency of
    // occurrence.
    unordered_map<string, int> unmap;

    // Iterate over all rows
    for (int i = 0; i < grid.size(); i++) {

        // Initialize an empty string s = ""
        string s = "";

        // Keep appending all the element
        // into string s
        for (int j = 0; j < grid[0].size(); j++) {
            s += to_string(grid[i][j]);
            s += "*";
        }

        // Increment the frequency count of
        // string s in map
        unmap[s]++;
    }

    // Initialize a result variable for
    // storing the number of pair such that
    // row and column are equal
    int result = 0;

    // Iterate over all the columns
    for (int j = 0; j < grid[0].size(); j++) {

        // Initialize an empty string s = ""
        string s = "";

        // Keep appending all the element
        // into string s
        for (int i = 0; i < grid.size(); i++) {
            s += to_string(grid[i][j]);
            s += "*";
        }

        // Add into result of frequency
        // count of s in map.
        result += unmap[s];
    }

    // Return the result
    return result;
}

// Driver code
int main()
{
    vector<vector<int> > arr = {
        { 2, 4, 1, 1 },
        { 4, 5, 6, 6 },
        { 1, 6, 4, 4 },
        { 1, 6, 4, 4 },
    };

    // Function Call
    cout << equalPairs(arr);

    return 0;
}
Java 
// Java code to implement the approach
import java.io.*;
import java.util.*;

class GFG {
    // Function to count the row-column pairs
    public static int equalPairs(int grid[][])
    {
        // Initialize a map for mapping all
        // column with their frequency of
        // occurrence.
        HashMap<String, Integer> unmap
            = new HashMap<String, Integer>();

        // Iterate over all rows
        for (int i = 0; i < grid.length; i++) {

            // Initialize an empty string s = ""
            String s = "";

            // Keep appending all the element
            // into string s
            for (int j = 0; j < grid[0].length; j++) {
                s += Integer.toString(grid[i][j]);
                s += "*";
            }

            // Increment the frequency count of
            // string s in map
            if (unmap.get(s) == null) {
                unmap.put(s, 1);
            }
            else {
                unmap.put(s, unmap.get(s) + 1);
            }
        }

        // Initialize a result variable for
        // storing the number of pair such that
        // row and column are equal
        int result = 0;

        // Iterate over all the columns
        for (int j = 0; j < grid[0].length; j++) {

            // Initialize an empty string s = ""
            String s = "";

            // Keep appending all the element
            // into string s
            for (int i = 0; i < grid.length; i++) {
                s += Integer.toString(grid[i][j]);
                s += "*";
            }

            // The condition check is required
            // for cases like the below
            // { 3,2,1},
            // { 1,7,6},
            // { 2,7,7},
            if (unmap.containsKey(s)) {
               result += unmap.get(s);
            }  
        }

        // Return the result
        return result;
    }

    // Driver Code
    public static void main(String[] args)
    {
        int arr[][] = {
            { 2, 4, 1, 1 },
            { 4, 5, 6, 6 },
            { 1, 6, 4, 4 },
            { 1, 6, 4, 4 },
        };

        // Function Call
        System.out.print(equalPairs(arr));
    }
}

// This code is contributed by Rohit Pradhan
Python 
# Python3 code to implement the approach

# Function to count the row-column pairs
def equalPairs(grid) :

    # Initialize a map for mapping all
    # column with their frequency of
    # occurrence.
    unmap = {};

    # Iterate over all rows
    for i in range(len(grid)) :

        # Initialize an empty string s = ""
        s = "";

        # Keep appending all the element
        # into string s
        for j in range(len(grid[0])) :
            s += str(grid[i][j]);
            s += "*";
        
        if s in unmap :
            # Increment the frequency count of
            # string s in map
            unmap[s] += 1;     
        else :
            unmap[s] = 1;


    # Initialize a result variable for
    # storing the number of pair such that
    # row and column are equal
    result = 0;

    # Iterate over all the columns
    for j in range(len(grid[0])) :

        # Initialize an empty string s = ""
        s = "";

        # Keep appending all the element
        # into string s
        for i in range(len(grid)) :
            s += str(grid[i][j]);
            s += "*";

        # Add into result of frequency
        # count of s in map.
        result += unmap[s];

    # Return the result
    return result;

# Driver code
if __name__ == "__main__" :

    arr = [
        [ 2, 4, 1, 1 ],
        [ 4, 5, 6, 6 ],
        [ 1, 6, 4, 4 ],
        [ 1, 6, 4, 4 ],
    ];

    # Function Call
    print(equalPairs(arr));

    # This code is contributed by AnkThon
C# 
// C# code to implement the approach
using System;
using System.Collections.Generic;
class GFG 
{
  
  // Function to count the row-column pairs
  static int equalPairs(int[, ] grid, int N, int M)
  {
    
    // Initialize a map for mapping all
    // column with their frequency of
    // occurrence.
    Dictionary<string, int> mp
      = new Dictionary<string, int>();
    
    // Iterate over all rows
    for (int i = 0; i < N; i++) {

      // Initialize an empty string s = ""
      string s = "";

      // Keep appending all the element
      // into string s
      for (int j = 0; j < M; j++) {
        s += grid[i, j].ToString();
        s += "*";
      }

      // Increment the frequency count of
      // string s in map

      if (mp.ContainsKey(s)) {
        int val = mp[s];
        mp.Remove(s);
        mp.Add(s, val + 1);
      }
      else
        mp.Add(s, 1);
    }

    // Initialize a result variable for
    // storing the number of pair such that
    // row and column are equal
    int result = 0;

    // Iterate over all the columns
    for (int j = 0; j < M; j++) {

      // Initialize an empty string s = ""
      string s = "";

      // Keep appending all the element
      // into string s
      for (int i = 0; i < N; i++) {
        s += grid[i, j].ToString();
        s += "*";
      }

      // Add into result of frequency
      // count of s in map.
      result += mp[s];
    }

    // Return the result
    return result;
  }
  static void Main()
  {
    int[, ] arr = {
      { 2, 4, 1, 1 },
      { 4, 5, 6, 6 },
      { 1, 6, 4, 4 },
      { 1, 6, 4, 4 },
    };

    // Function Call
    Console.Write(equalPairs(arr, 4, 4));
  }
}

// This code is contributed by garg28harsh.
JavaScript 
// JavaScript code for the above approach

// Function to count the row-column pairs
function equalPairs(grid)
{
    // Initialize a map for mapping all
    // column with their frequency of
    // occurrence.
    let unmap = new Map();

    // Iterate over all rows
    for (let i = 0; i < grid.length; i++) {

        // Initialize an empty string s = ""
        let s = "";

        // Keep appending all the element
        // into string s
        for (let j = 0; j < grid[0].length; j++) {
            s += (grid[i][j]).toString();
            s += "*";
        }

        // Increment the frequency count of
        // string s in map

        if (unmap.has(s)) {
            unmap.set(s, unmap.get(s) + 1)
        }
        else {
            unmap.set(s, 1)
        }
    }

    // Initialize a result variable for
    // storing the number of pair such that
    // row and column are equal
    let result = 0;

    // Iterate over all the columns
    for (let j = 0; j < grid[0].length; j++) {

        // Initialize an empty string s = ""
        let s = "";

        // Keep appending all the element
        // into string s
        for (let i = 0; i < grid.length; i++) {
            s += grid[i][j].toString();
            s += "*";
        }

        // Add into result of frequency
        // count of s in map.
        result += unmap.get(s);
    }

    // Return the result
    return result;
}

// Driver code

let arr = [
    [ 2, 4, 1, 1 ],
    [ 4, 5, 6, 6 ],
    [ 1, 6, 4, 4 ],
    [ 1, 6, 4, 4 ],
];

// Function Call
console.log(equalPairs(arr));

// This code is contributed by Potta Lokesh

Output
6

Time Complexity: O(N2)
Auxiliary Space: O(N2)

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