Rotate Matrix Elements in Java

In this article, we will understand how to rotate matrix elements using Java. A matrix is a representation of the elements in rows and columns. Matrix rotation is shifting the position of each element of the matrix by 1 position towards its right or left. We will be using two approaches: one where the matrix is rotated based on user input, and another where the matrix is defined within the code.

Problem Statement

Write a Java program to rotate matrix elements. Below is a demonstration of the same ?

Input

The matrix is defined as
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

Output

The matrix after one rotation:
5 1 2 3
9 10 6 4
13 11 7 8
14 15 16 12

Different approaches

Following are the different approaches to rotate matrix elements ?

• Using user input
• Using previously defined input
  

Using user input

The following are the steps to rotate matrix elements using user-based input ?

• First, we will import the Scanner class from java.util package.
• Take input from the user for matrix dimensions (Rows and Columns).
  
• Ask the user to input matrix elements row-wise and use m and n to represent rows and columns, and row and column to track current position.
• Rotation Process:
  
• Left to right along the first row.
  
• Top to bottom along the last column.
  
• Right to left across the last row.
  
• Bottom to top along the first column.
  
• Display the rotated matrix and print the matrix after one rotation.
  

Example

In the given example the input is being entered by the user based on a prompt ?

import java.util.Scanner;
public class RotateMatrix {
   static int Rows, Columns;
   public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      System.out.print("Enter the number of rows: ");
      Rows = sc.nextInt();
      System.out.print("Enter the number of columns: ");
      Columns = sc.nextInt();
      int input_matrix[][] = new int[Rows][Columns];
      System.out.println("Enter the elements of the matrix:");
      for (int i = 0; i < Rows; i++) {
         for (int j = 0; j < Columns; j++) {
            input_matrix[i][j] = sc.nextInt();
         }
      }
      System.out.println("The input matrix is defined as:");
      for (int i = 0; i < Rows; i++) {
         for (int j = 0; j < Columns; j++) {
            System.out.print(input_matrix[i][j] + " ");
         }
         System.out.print("\n");
      }
      int m = Rows, n = Columns;
      int row = 0, column = 0;
      int previous, current;
      while (row < m && column < n) {
         if (row + 1 == m || column + 1 == n)
            break;
         previous = input_matrix[row + 1][column];
         for (int i = column; i < n; i++) {
            current = input_matrix[row][i];
            input_matrix[row][i] = previous;
            previous = current;
         }
         row++;
         for (int i = row; i < m; i++) {
            current = input_matrix[i][n-1];
            input_matrix[i][n-1] = previous;
            previous = current;
         }
         n--;
         if (row < m) {
            for (int i = n-1; i >= column; i--) {
               current = input_matrix[m-1][i];
               input_matrix[m-1][i] = previous;
               previous = current;
            }
         }
         m--;
         if (column < n) {
            for (int i = m-1; i >= row; i--) {
               current = input_matrix[i][column];
               input_matrix[i][column] = previous;
               previous = current;
            }
         }
         column++;
      }
      System.out.println("\nThe matrix after one rotation:");
      for (int i = 0; i < Rows; i++) {
         for (int j = 0; j < Columns; j++) {
            System.out.print(input_matrix[i][j] + " ");
         }
         System.out.print("\n");
      }
      sc.close();
   }
}

Output

The input_matrix is defined as
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

The input_matrix after one rotation:
5 1 2 3
9 10 6 4
13 11 7 8
14 15 16 12

Using previously defined input

The following are the steps to rotate matrix elements using previously defined input ?

• First, we will define the matrix dimensions (Rows = 4, Columns = 4).
  
• Define a matrix with predefined values and print the input matrix.
• Call the Rotate_matrix() method, passing the matrix and its dimensions.
  
• Inside the Rotate_matrix() method: Set initial values for row, column, and previous/current variables.
• Use a while loop to rotate the matrix as long as the matrix is not reduced to a single row or column.
  
• Rotate the elements in the same order as the first program.
  
• Update the matrix in place.
  
• After the loop finishes, print the matrix after rotation.

Example

Here, the integer has been previously defined, and its value is accessed and displayed on the console ?

public class RotateMatrix {
   static int Rows = 4;
   static int Columns = 4;
   static void Rotate_matrix(int m,
   int n, int matrix[][]) {
      int row = 0, column = 0;
      int previous, current;
      while (row < m && column < n) {
         if (row + 1 == m || column + 1 == n)
            break;
         previous = matrix[row + 1][column];
         for (int i = column; i < n; i++) {
            current = matrix[row][i];
            matrix[row][i] = previous;
            previous = current;
         }
         row++;
         for (int i = row; i < m; i++) {
            current = matrix[i][n-1];
            matrix[i][n-1] = previous;
            previous = current;
         }
         n--;
         if (row < m) {
            for (int i = n-1; i >= column; i--) {
               current = matrix[m-1][i];
               matrix[m-1][i] = previous;
               previous = current;
            }
         }
         m--;
         if (column < n) {
            for (int i = m-1; i >= row; i--) {
               current = matrix[i][column];
               matrix[i][column] = previous;
               previous = current;
            }
         }
         column++;
      }
      System.out.println("\nThe matrix after one rotation: ");
      for (int i = 0; i < Rows; i++) {
         for (int j = 0; j < Columns; j++)
         System.out.print( matrix[i][j] + " ");
         System.out.print("\n");
      }
   }
   public static void main(String[] args) {
      int input_matrix[][] = {
         {1, 2, 3, 4},
         {5, 6, 7, 8},
         {9, 10, 11, 12},
         {13, 14, 15, 16}
      };
      System.out.println("The matrix is defined as ");
      for (int i = 0; i < Rows; i++) {
         for (int j = 0; j < Columns; j++)
         System.out.print( input_matrix[i][j] + " ");
         System.out.print("\n");
      }
      Rotate_matrix(Rows, Columns, input_matrix);
   }
}

Output

The matrix is defined as
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

The matrix after one rotation:
5 1 2 3
9 10 6 4
13 11 7 8
14 15 16 12