Find unique elements in a matrix

Last Updated : 24 Mar, 2023

Given a matrix mat[][] having n rows and m columns. We need to find unique elements in matrix i.e, those elements which are not repeated in the matrix or those elements whose frequency is 1.

Examples:

Input :  20  15  30  2
         2   3   5   30
         6   7   6   8
Output : 3  20  5  7  8  15 

Input :  1  2  3  
         5  6  2
         1  3  5
         6  2  2
Output : No unique element in the matrix

Follow these steps to find a unique element:

Create an empty hash table or dictionary.
Traverse through all the elements of the matrix
If element is present in the dictionary, then increment its count
Otherwise insert element with value = 1.

Implementation:

C++

// C++ program to find unique 
// element in matrix 
#include<bits/stdc++.h> 
using namespace std; 
#define R 4 
#define C 4 
  
// function that calculate unique element 
int unique(int mat[R][C], int n, int m) 
{ 
    int maximum = 0, flag = 0; 
    for(int i = 0; i < n; i++)  
        for(int j = 0; j < m; j++) 
            // Find maximum element in 
            // a matrix 
            if(maximum < mat[i][j]) 
                    maximum = mat[i][j]; 
  
    // Take 1-D array of (maximum + 1) 
    // size 
    int b[maximum + 1] = {0}; 
    for(int i = 0 ; i < n; i++) 
        for(int j = 0; j < m; j++) 
            b[(mat[i][j])]++; 
  
    //print unique element 
    for(int i = 1; i <= maximum; i++) 
        if(b[i] == 1) 
            cout << i << " "; 
            flag = 1; 
              
    if(!flag){ 
        cout << "No unique element in the matrix"; 
    } 
} 
  
// Driver program 
int main() 
{ 
    int mat[R][C] = {{ 1, 2, 3, 20}, 
                     {5, 6, 20, 25}, 
                     {1, 3, 5, 6}, 
                     {6, 7, 8, 15}}; 
                       
    // function that calculate unique element 
    unique(mat, R, C); 
    return 0; 
} 
  
// This code is contributed by Naman_Garg. 

Java

// Java program to find unique 
// element in matrix 
import java.util.*; 
class GFG 
{ 
static int R = 4, C = 4; 
  
// function that calculate  
// unique element 
static void unique(int mat[][],  
                   int n, int m) 
{ 
    int maximum = 0, flag = 0; 
    for(int i = 0; i < n; i++)  
        for(int j = 0; j < m; j++) 
          
            // Find maximum element  
            // in a matrix 
            if(maximum < mat[i][j]) 
                    maximum = mat[i][j]; 
  
    // Take 1-D array of  
    // (maximum + 1) size 
    int b[] = new int [maximum + 1]; 
    for(int i = 0 ; i < n; i++) 
        for(int j = 0; j < m; j++) 
            b[(mat[i][j])]++; 
  
    //print unique element 
    for(int i = 1; i <= maximum; i++) 
        if(b[i] == 1) 
            System.out.print(i + " "); 
            flag = 1; 
              
    if(flag == 0) 
    { 
        System.out.println("No unique element " +  
                                "in the matrix"); 
    } 
} 
  
// Driver Code 
public static void main(String args[]) 
{ 
    int mat[][] = {{1, 2, 3, 20}, 
                   {5, 6, 20, 25}, 
                   {1, 3, 5, 6}, 
                   {6, 7, 8, 15}}; 
                      
    // function that calculate  
    // unique element 
    unique(mat, R, C); 
} 
} 
  
// This code is contributed 
// by Arnab Kundu 

Python3

# Python 3 program to find unique 
# element in matrix 
def unique(mat, n, m): 
  
    maximum = 0; flag = 0
      
    for i in range(0, n): 
        for j in range(0, m): 
              
            # Find maximum element in 
            # a matrix 
            if(maximum < mat[i][j]): 
                maximum = mat[i][j]; 
  
    uniqueElementDict = [0] * (maximum + 1) 
  
    # loops to traverse through the matrix  
    for i in range(0, n): 
        for j in range(0, m): 
                uniqueElementDict[(mat[i][j])] += 1
  
    # Print all those keys whose count is 1 
    for key in range(maximum + 1): 
        if uniqueElementDict[key] == 1: 
            print (key, end = " ") 
            flag = 1
      
    if(flag == 0): 
        print("No unique element in the matrix") 
  
# Driver Code 
mat = [[1, 2, 3, 20],  
       [5, 6, 20, 25], 
       [1, 3, 5, 6], 
       [6, 7, 8, 15]] 
n = 4
m = 4
unique(mat, n, m) 

C#

// C# program to find unique  
// element in matrix 
using System; 
  
class GFG  
{  
static int R = 4, C = 4;  
  
// function that calculate  
// unique element  
static void unique(int [,]mat,  
                   int n, int m)  
{  
    int maximum = 0, flag = 0;  
    for(int i = 0; i < n; i++)  
        for(int j = 0; j < m; j++)  
          
            // Find maximum element  
            // in a matrix  
            if(maximum < mat[i, j])  
                    maximum = mat[i, j];  
  
    // Take 1-D array of  
    // (maximum + 1) size  
    int []b = new int [maximum + 1];  
    for(int i = 0 ; i < n; i++)  
        for(int j = 0; j < m; j++)  
            b[(mat[i, j])]++;  
  
    // print unique element  
    for(int i = 1; i <= maximum; i++)  
        if(b[i] == 1)  
            Console.Write(i + " ");  
            flag = 1;  
              
    if(flag == 0)  
    {  
        Console.WriteLine("No unique element " +  
                               "in the matrix");  
    }  
}  
  
// Driver Code  
public static void Main()  
{  
    int [,]mat = {{1, 2, 3, 20},  
                  {5, 6, 20, 25},  
                  {1, 3, 5, 6},  
                  {6, 7, 8, 15}};  
                      
    // function that calculate  
    // unique element  
    unique(mat, R, C);  
}  
}  
  
// This code is contributed  
// by Subhadeep 

PHP

<?php 
// PHP program to find unique 
// element in matrix 
  
$R = 4; 
$C = 4; 
  
// function that calculate unique element 
function unique($mat, $n, $m) 
{ 
    $maximum = 0; 
    $flag = 0; 
    for($i = 0; $i < $n; $i++)  
        for($j = 0; $j < $m; $j++) 
          
            // Find maximum element in 
            // a matrix 
            if($maximum < $mat[$i][$j]) 
                    $maximum = $mat[$i][$j]; 
  
    // Take 1-D array of (maximum + 1) 
    // size 
    $b = array(); 
    for($j = 0; $j < $maximum + 1; $j++) 
        $b[$j] = 0; 
      
    for($i = 0 ; $i < $n; $i++) 
        for($j = 0; $j < $m; $j++) 
            $b[$mat[$i][$j]]++; 
  
    // print unique element 
    for($i = 1; $i <= $maximum; $i++) 
        if($b[$i] == 1) 
            echo "$i "; 
            $flag = 1; 
              
    if(!$flag) 
    { 
        echo "No unique element in the matrix"; 
    } 
} 
  
// Driver Code 
$mat = array(array(1, 2, 3, 20), 
             array(5, 6, 20, 25), 
             array(1, 3, 5, 6), 
             array(6, 7, 8, 15)); 
                  
// function that calculate unique element 
unique($mat, $R, $C); 
  
// This code is contributed by iAyushRaj 
?> 

Javascript

<script> 
  
// Javascript program to find unique  
// element in matrix 
var R = 4, C = 4;  
  
// Function that calculate  
// unique element  
function unique(mat, n, m)  
{ 
    var maximum = 0, flag = 0;  
    for(var i = 0; i < n; i++)  
        for(var j = 0; j < m; j++)  
          
            // Find maximum element  
            // in a matrix  
            if (maximum < mat[i][j])  
                maximum = mat[i][j];  
  
    // Take 1-D array of  
    // (maximum + 1) size  
    var b = Array(maximum+1).fill(0); 
    for(var i = 0 ; i < n; i++)  
        for(var j = 0; j < m; j++)  
            b[(mat[i][j])]++;  
  
    // Print unique element  
    for(var i = 1; i <= maximum; i++)  
        if (b[i] == 1)  
            document.write(i + " ");  
            flag = 1;  
              
    if (flag == 0)  
    {  
        document.write("No unique element " +  
                       "in the matrix<br>");  
    }  
}  
  
// Driver Code  
var mat = [ [ 1, 2, 3, 20 ],  
            [ 5, 6, 20, 25 ],  
            [ 1, 3, 5, 6 ],  
            [ 6, 7, 8, 15 ] ];  
                  
// Function that calculate  
// unique element  
unique(mat, R, C);  
  
// This code is contributed by rrrtnx 
  
</script>

Output

2 7 8 15 25

Complexity Analysis:

Time Complexity: O(m*n) where m is the number of rows & n is the number of columns.
Auxiliary Space: O(max(matrix)).

Method – 2: Using HashMap

This approach uses a hashmap instead of creating a hashtable of size max element + 1.

Implementation

C++

// C++ program to find unique element in matrix 
#include <bits/stdc++.h> 
using namespace std; 
#define R 4 
#define C 4 
  
// function that calculate unique element 
int unique(int mat[R][C], int n, int m) 
{ 
    // declare map for hashing 
    unordered_map<int, int> mp; 
  
    for (int i = 0; i < n; i++) 
        for (int j = 0; j < m; j++) 
            // increase freq of mat[i][j] in map 
            mp[(mat[i][j])]++; 
  
    int flag = false; 
    // print unique element 
    for (auto p : mp) { 
        if (p.second == 1) { 
            cout << p.first << " "; 
            flag = 1; 
        } 
    } 
  
    if (!flag) { 
        cout << "No unique element in the matrix"; 
    } 
} 
  
// Driver program 
int main() 
{ 
    int mat[R][C] = { { 1, 2, 3, 20 }, 
                      { 5, 6, 20, 25 }, 
                      { 1, 3, 5, 6 }, 
                      { 6, 7, 8, 15 } }; 
  
    // function that calculate unique element 
    unique(mat, R, C); 
    return 0; 
}

Java

// Java program to find unique element in matrix 
import java.util.*; 
  
// Main class 
public class GFG { 
  
  // function that calculate unique element 
  public static void unique(int mat[][], int R, int C) { 
  
    // declare map for hashing 
    Map<Integer, Integer> map = new HashMap<>(); 
  
    for (int i = 0; i < R; i++) { 
      for (int j = 0; j < C; j++) { 
        // increase freq of mat[i][j] in map 
        if (map.containsKey(mat[i][j])) { 
          map.put(mat[i][j], 1 + map.get(mat[i][j])); 
        } else { 
          map.put(mat[i][j], 1); 
        } 
      } 
    } 
  
    int flag = 0; 
  
    // print unique element 
    for (Map.Entry<Integer, Integer> e : map.entrySet()) { 
      if (e.getValue() == 1) { 
        // Printing key 
        System.out.print(e.getKey() + " "); 
        flag = 1; 
      } 
    } 
    if (flag == 0) { 
      System.out.println("No unique element in the matrix"); 
    } 
  } 
  
  // Driver program 
  public static void main(String[] args) { 
    int R = 4; 
    int C = 4; 
    int mat[][] = { { 1, 2, 3, 20 }, 
                   { 5, 6, 20, 25 }, 
                   { 1, 3, 5, 6 }, 
                   { 6, 7, 8, 15 } 
                  }; 
  
    // function that calculate unique element 
    unique(mat, R, C); 
  } 
} 
  
// This code is contributed by aadityaburujwale.

Python3

# Python program to find unique element in matrix 
  
# function that calculate unique element 
def unique(mat, r, c) -> int: 
    
    # declare map for hashing 
    mp = {} 
    for i in range(r): 
        for j in range(c): 
            
            # increase freq of mat[i][j] in map 
            if mat[i][j] not in mp: 
                mp[(mat[i][j])] = 1
            else: 
                mp[(mat[i][j])] += 1
    flag = False
      
    # print unique element 
    for p in mp: 
        if mp[p] == 1: 
            print(p, end=" ") 
            flag = True
    if flag == False: 
        print("No unique element in the matrix") 
  
  
# Driver program 
if __name__ == "__main__": 
    mat = [[1, 2, 3, 20], [5, 6, 20, 25], [1, 3, 5, 6], [6, 7, 8, 15]] 
      
    # function that calculate unique element 
    unique(mat, 4, 4) 
  
    # This code is contributed by ajaymakvana

C#

// C# program to find unique element in matrix 
using System; 
using System.Collections.Generic; 
  
public class GFG  
{ 
  
  // function that calculate unique element 
  public static void unique(int[, ] mat, int R, int C) 
  { 
  
    // declare map for hashing 
    Dictionary<int, int> map = new Dictionary<int, int>(); 
  
    for (int i = 0; i < R; i++) { 
      for (int j = 0; j < C; j++) { 
        // increase freq of mat[i][j] in map 
        if (map.ContainsKey(mat[i, j])) { 
          map[(mat[i, j])] = 1 + map[(mat[i, j])]; 
        } 
        else { 
          map[(mat[i, j])] = 1; 
        } 
      } 
    } 
  
    int flag = 0; 
  
    // print unique element 
    foreach(KeyValuePair<int, int> e in map) 
    { 
  
      // do something with entry.Value or entry.Key 
      if (e.Value == 1)  
      { 
  
        // Printing key 
        Console.Write(e.Key + " "); 
        flag = 1; 
      } 
    } 
    if (flag == 0) { 
      Console.WriteLine( 
        "No unique element in the matrix"); 
    } 
  } 
  
  // Driver program 
  public static void Main(string[] args) 
  { 
    int R = 4; 
    int C = 4; 
    int[, ] mat = { { 1, 2, 3, 20 }, 
                   { 5, 6, 20, 25 }, 
                   { 1, 3, 5, 6 }, 
                   { 6, 7, 8, 15 } }; 
  
    // function that calculate unique element 
    unique(mat, R, C); 
  } 
} 
  
// This code is contributed by ajaymakavana.

Javascript

// Javascript program to find unique element in matrix 
var R = 4; 
var C = 4; 
  
// function that calculate unique element 
function unique(mat, n, m) { 
    // declare map for hashing 
    const mp = new Map(); 
  
    for (var i = 0; i < n; i++) { 
        for (var j = 0; j < m; j++) { 
            // increase freq of mat[i][j] in map 
            if (mp.has(mat[i][j])) { 
                mp.set(mat[i][j], 1 + mp.get(mat[i][j])); 
            } else { 
                mp.set(mat[i][j], 1); 
            } 
        } 
    } 
  
    var flag = false; 
      
    // print unique element 
    for (const [key, value] of mp) { 
        // console.log(`${key} = ${value}`); 
        if (value == 1) { 
            console.log(`${key}`); 
            flag = true; 
        } 
    } 
  
    if (!flag) { 
        console.log("No unique element in the matrix"); 
    } 
} 
  
// Driver Code  
var mat = [ 
    [1, 2, 3, 20], 
    [5, 6, 20, 25], 
    [1, 3, 5, 6], 
    [6, 7, 8, 15] 
]; 
  
// Function that calculate unique element  
unique(mat, R, C); 
  
// This code is contributed by ajaymakvana.

Output

2 7 8 15 25

Time Complexity: O(R*C)
Auxiliary Space: O(R*C)

Suggest improvement

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Basic Operations on Matrix

Easy problems on Matrix

Intermediate problems on Matrix

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Find unique elements in a matrix

C++

Java

Python3

C#

PHP

Javascript

C++

Java

Python3

C#

Javascript

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