Java Program to Print Common Elements in all Rows of a Matrix

In the previous article, we have seen Java Program to Check Diagonally Dominant Matrix

In this article we are going to see how we can write a program to find common element in all row of a given matrix.

Java Program to Print Common Elements in all Rows of a Matrix

A 3*3 Matrix is having 3 rows and 3 columns where this 3*3 represents the dimension of the matrix. Means there are 3*3 i.e. total 9 elements in a 3*3 Matrix.

Let’s understand it in more simpler way.

                   | A00   A01   A02 |
Matrix A =  | A10   A11   A12 |
                   | A20   A21   A22 | 3*3

Matrix A represents a 3*3 matrix.
‘A‘ represents the matrix element
‘Aij‘ represents the matrix element at it’s matrix position/index.
‘i‘ represents the row index
‘j‘ represents the column index
Means A00=Aij where i=0 and j=0, A01=aij where i=0 and j=1 and like this.
Here we have started row value from 0 and column value from 0.

Let’s see different ways to common element in all row of a given matrix.

By Static Initialization of Array Elements
By Dynamic Initialization of Array Elements

Method-1: Java Program to Print Common Elements in all Rows of a Matrix By Static Initialization of Array Elements

Approach :

Declare and Initialize a matrix.
Define ele with elements as keys and their count as values.
Insert all elements of first row into ele with 1 as their values.
For remaining rows, check presence of each element in ele.
If element is present in ele and its count is equal to ‘x’, then increment its count by 1.
Print ele having common elements.

Program :

import java.util.*;
import java.util.Map.Entry;

public class Main 
{
   public static void main(String args[])
   {
      int mat[][] = { { 1, 2, 3 },{ 4, 3, 1 },{ 1, 0, 3 } }; 
      
        //Define ele with elements as keys and their count as values
        HashMap<Integer, Integer> ele = new HashMap<>();
        
        //Insert all elements of first row into ele with 1 as their values
        for (int y = 0; y < 3; y++)
            ele.put(mat[0][y], 1);
            
        //For remaining rows, check presence of each element in ele
        for (int x = 1; x < 3; x++) 
            for (int y = 0; y < 3 ; y++) 
                //If element is present in ele and it's count is equal to 'x',
                //then increment its count by 1
                if(ele.containsKey(mat[x][y]) && ele.get(mat[x][y]) == x)
                        ele.put(mat[x][y], x+1);
                        
        //Printing ele having common elements
        Set<Entry<Integer, Integer>> en = ele.entrySet();
        System.out.println("Common Elements In All Rows : ");
        for (Entry<Integer, Integer> e : en) 
            if (e.getValue() == 3) 
                System.out.print(e.getKey() + " ");
    } 
}

Output:

Common Elements In All Rows : 
1 3

Method-2: Java Program to Print Common Elements in all Rows of a Matrix By Dynamic Initialization of Array Elements

Approach:

Take user input of a matrix.
Define ele with elements as keys and their count as values.
Insert all elements of first row into ele with 1 as their values.
For remaining rows, check presence of each element in ele.
If element is present in ele and its count is equal to ‘x’, then increment its count by 1.
Print ele having common elements.

Program:

import java.util.*;
import java.util.Map.Entry;
public class Main 
{
   public static void main(String args[])
   {
       Scanner sc = new Scanner(System.in);
       
        // Initializing the 3X3 matrix i.e. 2D array
        int mat[][] = new int[3][3];
        int row, col ;
        
        // Taking matrix input
        System.out.println("\nEnter matrix elements");
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
                mat[row][col] = sc.nextInt();
                
        //Define ele with elements as keys and their count as values
        HashMap<Integer, Integer> ele = new HashMap<>();
        
        //Insert all elements of first row into ele with 1 as their values
        for (int y = 0; y < 3; y++)
            ele.put(mat[0][y], 1);
            
        //For remaining rows, check presence of each element in ele
        for (int x = 1; x < 3; x++) 
            for (int y = 0; y < 3 ; y++) 
                //If element is present in ele and it's count is equal to 'x',
                //then increment its count by 1
                if(ele.containsKey(mat[x][y]) && ele.get(mat[x][y]) == x)
                        ele.put(mat[x][y], x+1);
                        
        //Printing ele having common elements
        Set<Entry<Integer, Integer>> en = ele.entrySet();
        System.out.println("Common Elements In All Rows : ");
        for (Entry<Integer, Integer> e : en) 
            if (e.getValue() == 3) 
                System.out.print(e.getKey() + " ");
    } 
}

Output:

Enter matrix elements
Common Elements In All Rows : 
1 3

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