Interchange Diagonal Elements Java Program

In this section, we will learn how to interchange diagonals of a matrix through a Java program. It is usually asked in Java interviews and academics.

Consider the above 4*4 matrix whose size is n.

In the above matrix, we have to swap the following indexes to interchange the diagonal.

[0][0] swap with [0][3]

[1][1] swap with [1][2]

[2][2] swap with [2][1]

[3][3] swap with [3][0]

From the above, we observe that the row index of both sides is the same and the only change in column index. If we look carefully at the column index, we found the pattern that is on the left side column index is increasing by 1 and in the right side, column index is decreasing by 1.

So, we can create a formula to get the right-side column index i.e. n-i-1.

For the above logic, we require a loop in which we swap the diagonal elements.

for(i=0; i<n-1;i++)
{
swap(a[i][i], a[i][n-i-1]);
}

Note: To perform the diagonal interchange, the number of rows and columns must be the same.

Algorithm

Declare variables for the matrix size.
Ask the user to initialize the matrix rows and columns
Check if the number of rows and columns are equal or not.
If equal, then ask the user to initialize the matrix.
Print the original matrix.
Swap the diagonal elements.
Print the diagonals interchanged matrix.
If rows and columns are not equal, print the same message.

Let's implement the above logic in a Java program.

In the following program, we have taken the input of a 3*3 matrix. After that, we have printed the original matrix, performed the swapping of elements, and at last printed the diagonal interchanged matrix.

InterchangeDiagonal.java

import java.util.Scanner;
public class InterchangeDiagonal
{
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter rows and column of the matrix: ");
        //reading the number of rows and column from the user
        int n=sc.nextInt();
        //creating a matrix of n*n
        int a[][] = new int [n][n];
        //input matrix elements 
        System.out.println("Enter the elements of the matrix: ");
        //loop for rows
        for(int i=0; i<n; i++)
        {
            //loop for column
            for(int j=0; j<n; j++)
            {
                //reading matrix elements
                a[i][j]=sc.nextInt();
            }
        }
        //printing the original matrix
        System.out.println("\nOriginal matrix: \n");
        for(int i=0; i<n; i++)
        {
            for(int j=0; j<n; j++)
            {
                 System.out.print(a[i][j]+"\t");
            }
            System.out.println(" ");
        }
        //swapping elements 
        for(int i=0; i<n; i++)
        {
            int temp = a[i][i];
            a[i][i] = a[i][n-i-1];
            a[i][n-i-1] = temp;
        }
        //prints the diagonal interchanged matrix
        System.out.println("\nDiagonal Interchanged Matrix: \n");
        for(int i=0; i<n; i++)
        {
            for(int j=0; j<n; j++)
            {
                 System.out.print(a[i][j]+"\t");
            }
            System.out.println(" ");
        }
    }
}

Output: