Common elements in all rows of a given matrix in Java

May 4, 2022

Common elements in all row of a given matrix in Java

Here, in this page we will discuss the program to find the common elements in all row of a given matrix in Java Programming language. We will discuss algorithm along it’s code.

Common elements in all row of a given matrix in Java

Method 1 :

In this algorithm we will check for every element in first row, if that is present in other rows or not.

  • For checking the presence, take one variable count.
  • Now, run a loop from index 1 to M.
  • Take a variable flag =0;
  • Now, run a loop from index 0 to N, if (x==mat[i][j]) set flag =1 and break the loop.
  • After coming out from loop check if(flag==1) set, count++.
  • At last, check if count == M-1, print that value.

Time and Space Complexity :

  • Time complexity: O(M*M*N)
  • Space complexity: O(1)
Common Element in all rows of the matrix

Method 1 : Code in Java

Run 
class Main
{
   
    public static void main(String args[])
    {
        int mat[][] = {{10, 20, 30, 40},
                       {15, 25, 35, 30},
                       {27, 30, 37, 48},
                       {32, 33, 39, 30}};
        
        int N=4, M=4;
        
        for (int j = 0; j < N; j++){   
            int x = mat[0][j], count = 0;
            
            for (int i = 1; i < M; i++){
                int flag = 0;
                    for(int k = 0; k < N; k++){
                        if(x==mat[i][k]){
                            flag = 1;
                            mat[i][k] = -1;
                            break;
                        }        
                    }
                if(flag==1){
                    count++;   
            }
        }
        
        if (count==M-1)
           System.out.print(x);
            
        }
    }
}

Output :

30

Method 2:

  • In this method we will use map.
  • We initially insert all elements of the first row in an map.
  • For every other element in remaining rows, we check if it is present in the map.
  • If it is present in the map and is not duplicated in current row, we increment count of the element in map by 1, else we ignore the element.
  • If the currently traversed row is the last row, we print the element if it has appeared m-1 times before. 

Method 2 : Code in Java

Run 
import java.util.*;
 
class Main
{
    static int M = 4;
    static int N =5;
     
    static void printCommonElements(int mat[][])
    {
     
        Map<Integer,Integer> mp = new HashMap<>();
         
        for (int j = 0; j < N; j++)
            mp.put(mat[0][j],1);
             
        for (int i = 1; i < M; i++)
        {
            for (int j = 0; j < N; j++)
            {
                if (mp.get(mat[i][j]) != null && mp.get(mat[i][j]) == i)
                {
                    mp.put(mat[i][j], i + 1);
                    if (i == M - 1)
                        System.out.print(mat[i][j] + " ");
                }
            }
        }
    }
    public static void main(String[] args)
    {
        int mat[][] =
        {
            {1, 2, 1, 4, 8},
            {3, 7, 8, 5, 1},
            {8, 7, 7, 3, 1},
            {8, 1, 2, 7, 9},
        };
     
        printCommonElements(mat);
    }
}

Output :

8 1