Java Program to Rotate matrix by 45 degrees

Given a matrix mat[][] of size N*N, the task is to rotate the matrix by 45 degrees and print the matrix.

Examples:

Input: N = 6, 
mat[][] = {{3, 4, 5, 1, 5, 9, 5}, 
               {6, 9, 8, 7, 2, 5, 2},  
               {1, 5, 9, 7, 5, 3, 2}, 
               {4, 7, 8, 9, 3, 5, 2}, 
               {4, 5, 2, 9, 5, 6, 2}, 
               {4, 5, 7, 2, 9, 8, 3}}
Output:
 3
      6 4
    1 9 5
   4 5 8 1
  4 7 9 7 5
4 5 8 7 2 9
  5 2 9 5 5
   7 9 3 3
    2 5 5
     9 6
      8

Input: N = 4, 
mat[][] = {{2, 5, 7, 2}, 
                {9, 1, 4, 3}, 
                {5, 8, 2, 3}, 
                {6, 4, 6, 3}}

Output:
    2
  9 5
 5 1 7
6 8 4 2
 4 2 3
  6 3
   3 

Approach: Follow the steps given below in order to solve the problem:

1. Store the diagonal elements in a list using a counter variable.
2. Print the number of spaces required to make the output look like the desired pattern.
3. Print the list elements after reversing the list.
4. Traverse through only diagonal elements to optimize the time taken by the operation.

Below is the implementation of the above approach:

Java

// Java program for
// the above approach
import java.util.*;
class GFG{

// Function to rotate
// matrix by 45 degree
static void matrix(int n, int m,
                   int [][]li)
{
  // Counter Variable
  int ctr = 0;

  while (ctr < 2 * n - 1)
  {
    for(int i = 0; i < Math.abs(n - ctr - 1);
            i++)
    {
      System.out.print(" ");
    }

    Vector<Integer> lst = new Vector<Integer>();

    // Iterate [0, m]
    for(int i = 0; i < m; i++)
    {
      // Iterate [0, n]
      for(int j = 0; j < n; j++)
      {
        // Diagonal Elements
        // Condition
        if (i + j == ctr)
        {
          // Appending the
          // Diagonal Elements
          lst.add(li[i][j]);
        }
      }
    }

    // Printing reversed Diagonal
    // Elements
    for(int i = lst.size() - 1; i >= 0; i--)
    {
      System.out.print(lst.get(i) + " ");
    }

    System.out.println();
    ctr += 1;
  }
}

// Driver code
public static void main(String[] args)
{
  // Dimensions of Matrix
  int n = 8;
  int m = n;

  // Given matrix
  int[][] li = {{4, 5, 6, 9, 8, 7, 1, 4},
                {1, 5, 9, 7, 5, 3, 1, 6},
                {7, 5, 3, 1, 5, 9, 8, 0},
                {6, 5, 4, 7, 8, 9, 3, 7},
                {3, 5, 6, 4, 8, 9, 2, 1},
                {3, 1, 6, 4, 7, 9, 5, 0},
                {8, 0, 7, 2, 3, 1, 0, 8},
                {7, 5, 3, 1, 5, 9, 8, 5}};

  // Function call
  matrix(n, m, li);
}
}

// This code is contributed by Princi Singh

Output:

       4
      1 5
     7 5 6
    6 5 9 9
   3 5 3 7 8
  3 5 4 1 5 7
 8 1 6 7 5 3 1
7 0 6 4 8 9 1 4
 5 7 4 8 9 8 6
  3 2 7 9 3 0
   1 3 9 2 7
    5 1 5 1
     9 0 0
      8 8
       5

Time Complexity: O(N²)
Auxiliary Space: O(1)

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