Java Program to Rotate all Matrix elements except the diagonal K times by 90 degrees in clockwise direction

Given a square matrix mat[][] of dimension N and an integer K, the task is to rotate the matrix by 90 degrees K times without changing the position of the diagonal elements.

Examples:

Input: mat[][] = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}, {11, 12, 13, 14, 15}, {16, 17, 18, 19, 20}, {21, 22, 23, 24, 25}}, K = 1
Output:
 1 16 11 6 5  
 22 7 12 9 2
 23 18 13 8 3
 24 17 14 19 4
 21 20 15 10 25

Input: mat[][] = {{10, 11}, {12, 13}}, K = 2
Output:
10 11
12 13

Approach: The given problem can be solved by using the idea discussed in this article and the fact that the matrix restores after performing clockwise rotation 4 times. Follow the below steps to solve the given problem:

• Update the value of K as K % 4.
• Iterate until K is a positive and perform the following steps:
  • Traverse the matrix, for i over the range [0, N / 2) and j over the range[0, N – i – 1) and perform the following steps:
  • If the value of i != j and (i + j) != (N – 1), then perform the following steps:
    • Store the value of mat[i][j] in a temporary variable temp.
    • Update the value of mat[i][j] as mat[N – 1 – j][i].
    • Update the value of mat[N – 1 – j][i] as mat[N – 1 -i][N – 1 – j].
    • Update the value of mat[N – 1  – i][N – 1 – j] as mat[j][N – 1 – i].
    • Update the value of mat[j][N – 1 – i] as temp.
• After completing the above steps, print the updated matrix obtained.

Below is the implementation of the above approach:

Java

// Java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;

public class GFG {

    // Function to print the matrix
    static void print(int mat[][])
    {
        // Iterate over the rows
        for (int i = 0; i < mat.length; i++) {

            // Iterate over the columns
            for (int j = 0; j < mat[0].length; j++)

                // Print the value
                System.out.print(mat[i][j] + " ");

            System.out.println();
        }
    }

    // Function to perform the swapping of
    // matrix elements in clockwise manner
    static void performSwap(int mat[][], int i, int j)
    {
        int N = mat.length;

        // Stores the last row
        int ei = N - 1 - i;

        // Stores the last column
        int ej = N - 1 - j;

        // Perform the swaps
        int temp = mat[i][j];
        mat[i][j] = mat[ej][i];
        mat[ej][i] = mat[ei][ej];
        mat[ei][ej] = mat[j][ei];
        mat[j][ei] = temp;
    }

    // Function to rotate non - diagonal
    // elements of the matrix K times in
    // clockwise direction
    static void rotate(int mat[][], int N, int K)
    {
        // Update K to K % 4
        K = K % 4;

        // Iterate until K is positive
        while (K-- > 0) {

            // Iterate each up to N/2-th row
            for (int i = 0; i < N / 2; i++) {

                // Iterate each column
                // from i to N - i - 1
                for (int j = i; j < N - i - 1; j++) {

                    // Check if the element
                    // at i, j is not a
                    // diagonal element
                    if (i != j && (i + j) != N - 1) {

                        // Perform the swapping
                        performSwap(mat, i, j);
                    }
                }
            }
        }

        // Print the matrix
        print(mat);
    }

    // Driver Code
    public static void main(String[] args)
    {

        int K = 5;
        int mat[][] = {
            { 1, 2, 3, 4 },
            { 6, 7, 8, 9 },
            { 11, 12, 13, 14 },
            { 16, 17, 18, 19 },
        };

        int N = mat.length;
        rotate(mat, N, K);
    }
}

// This code is contributed by Kingash.

Output:

  1 11  6  4
 17  7  8  2
 18 12 13  3
 16 14  9 19

Time Complexity: O(N³) since using three inner loop one while and two for loop
Auxiliary Space: O(1)

Please refer complete article on Rotate all Matrix elements except the diagonal K times by 90 degrees in clockwise direction for more details!