Question

[CS]

WAP to accept m×n matric, shift each row 1 step downward.

Sample Input:-
Enter no. of rows and columns
4
5
Enter elements of 3×4 matric
1 2 3 4 5
2 4 6 8 0
3 6 9 0 3
4 8 0 4 8

Required Output:-

4 8 0 4 8
1 2 3 4 5
2 4 6 8 0
3 6 9 0 3​

Answer 1

Approach 1:

In this approach, we will copy the last row of the matrix and store the values in another array.

Consider a matrix A -

$\tt>> A = \left[\begin{array}{ccc}\tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\\ \tt7&\tt8&\tt9\end{array}\right]$

Here, we will store elements of the last row into another array -

$\tt >> B = [7, 8, 9]$

Now we will shift elements down.

$\tt>> A = \left[\begin{array}{ccc}\\ \tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\end{array}\right]$

Now, we will add the elements of b to the first row of matrix A.

$\tt>> A = \left[\begin{array}{ccc}\tt7&\tt8&\tt9\\ \tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\end{array}\right]$

So, the elements are shifted down. Here comes the co‎de.

import java.util.*;

public class MatrixRowShiftUsingArray{

   public static void main(String s[]){

       Scanner sc=new Scanner(System.in);

       int rows,cols,i,j;

       System.out.print("How many rows: ");

       rows=sc.nextInt();

       System.out.print("How many cols: ");

       cols=sc.nextInt();

       int a[][]=new int[rows][cols];

       int b[]=new int[cols];

       System.out.println("Enter elements...");

       for(i=0;i<rows;i++){

           for(j=0;j<cols;j++){

               System.out.printf("a[%d][%d] >> ",i,j);

               a[i][j]=sc.nextInt();

           }

       }

       System.out.println("\nGiven Matrix:");

       displayMatrix(a);

      // Modification starts.

       for(i=rows-1,j=0;j<cols;j++)

           b[j]=a[i][j];

       for(i=rows-2;i>=0;i--){

           for(j=0;j<cols;j++){

               a[i+1][j]=a[i][j];

           }

       }

       for(j=0;j<cols;j++){

           a[0][j]=b[j];

       }

       System.out.println("\nMatrix After Modification:");

       displayMatrix(a);

   }  

   static void displayMatrix(int a[][]){

       for(int x[]:a){

           for(int y:x)

               System.out.print(y+" ");

           System.out.println();

       }

   }

}

Note: The displayMatrix(a[][]) function is created to avoid repetition of co‎de.

Approach 2:

Here, only 1 matrix is needed for the modification.

Consider the 3 x 4 matrix A -

$\tt>> A = \left[\begin{array}{ccc}\tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\\ \tt7&\tt8&\tt9\\ \tt5&\tt0&\tt5\end{array}\right]$

Here, we will swap the first row with 2nd, 3rd and 4th row.

After first swap (1st with second),

$\tt>> A = \left[\begin{array}{ccc}\tt4&\tt5&\tt6\\ \tt1&\tt2&\tt3\\ \tt7&\tt8&\tt9\\ \tt5&\tt0&\tt5\end{array}\right]$

After second swap (1st with third),

$\tt>> A = \left[\begin{array}{ccc}\tt7&\tt8&\tt9\\ \tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\\ \tt5&\tt0&\tt5\end{array}\right]$

After third swap (1st with fourth),

$\tt>> A = \left[\begin{array}{ccc}\tt5&\tt0&\tt5\\ \tt1&\tt2&\tt3\\ \tt4&\tt5&\tt6\\ \tt7&\tt8&\tt9\end{array}\right]$

Hence, our matrix is modified. Here comes the co‎de for this.

import java.util.*;

public class MatrixRowShiftPart2{

   public static void main(String s[]){

       Scanner sc=new Scanner(System.in);

       int rows,cols,i,j,t=1,y;

       System.out.print("How many rows: ");

       rows=sc.nextInt();

       System.out.print("How many cols: ");

       cols=sc.nextInt();

       int a[][]=new int[rows][cols];

       System.out.println("Enter array elements...");

       for(i=0;i<rows;i++){

           for(j=0;j<cols;j++){

               System.out.printf("a[%d][%d] >> ",i,j);

               a[i][j]=sc.nextInt();

           }

       }

       System.out.println("\nGiven Matrix: ");

       displayMatrix(a);

       for(i=0;i<rows-1;i++,t++){

           for(j=0;j<cols;j++){

               y=a[0][j];

               a[0][j]=a[t][j];

               a[t][j]=y;

           }

       }

       System.out.println("\nModified Matrix:");

       displayMatrix(a);

   }

   static void displayMatrix(int a[][]){

       for(int x[]:a){

           for(int y:x)

               System.out.print(y+" ");

           System.out.println();

       }

   }

}

See the attachment for output.