Swap major and minor diagonals of a square matrix

Given a square matrix, swap the element of major and minor diagonals.

Major Diagonal Elements of a Matrix :
The Major Diagonal Elements are the ones that occur from Top Left of Matrix Down To Bottom Right Corner. The Major Diagonal is also known as Main Diagonal or Primary Diagonal.

Minor Diagonal Elements of a Matrix :
The Minor Diagonal Elements are the ones that occur from Top Right of Matrix Down To Bottom Left Corner. Also known as Secondary Diagonal.

Example :

Input : 0 1 2
        3 4 5
        6 7 8

Output : 2 1 0
         3 4 5
         8 7 6

Approach: The Simple thing one should know is that the indexes of Primary or Major diagonal are same i.e. lets say A is matrix then A[1][1] will be a Major Diagonal element and sum of indexes of Minor Diagonal is equal to size of Matrix. Lets say A is a matrix of size 3 then A[1][2] will be Minor Diagonal element.

Below is the implementation of above approach : 

C++

// CPP Program to swap diagonal of a matrix
#include <bits/stdc++.h>
using namespace std;

// size of square matrix
#define N 3

// Function to swap diagonal of matrix
void swapDiagonal(int matrix[][N]) {
  for (int i = 0; i < N; i++)
    swap(matrix[i][i], matrix[i][N - i - 1]);
}

// Driver Code
int main() {
  int matrix[N][N] = {{0, 1, 2},
                      {3, 4, 5},
                      {6, 7, 8}};

  swapDiagonal(matrix);

  // Displaying modified matrix
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++)
      cout << matrix[i][j] << " ";
    cout << endl;
  }

  return 0;
}

Java

// Java implementation to swap
// diagonal of a matrix
import java.io.*;

class Gfg {
static int N = 3;

// Function to swap diagonal of matrix
static void swapDiagonal(int matrix[][]) {
    for (int i = 0; i < N; i++) {
    int temp = matrix[i][i];
    matrix[i][i] = matrix[i][N - i - 1];
    matrix[i][N - i - 1] = temp;
    }
}

// Driver function
public static void main(String arg[]) {
    int matrix[][] = {{0, 1, 2},
                      {3, 4, 5},
                      {6, 7, 8}};

    swapDiagonal(matrix);

    // Displaying modified matrix
    for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++)
        System.out.print(matrix[i][j] + " ");
    System.out.println();
    }
}
}

// This code is contributed by Anant Agarwal.

Python3

# Python3 Program to swap diagonal of a matrix

# size of square matrix
N = 3

# Function to swap diagonal of matrix
def swapDiagonal(matrix):

    for i in range(N):

        matrix[i][i], matrix[i][N-i-1] = \
            matrix[i][N-i-1], matrix[i][i]


# Driver Code
matrix = [[0, 1, 2],
          [3, 4, 5],
          [6, 7, 8]]

# swap diagonals of matrix
swapDiagonal(matrix);

# Displaying modified matrix
for i in range(N):
    for j in range(N):
        print(matrix[i][j], end = ' ')
    print()

C#

// C# implementation to swap
// diagonal of a matrix
using System;

class Gfg {

    static int N = 3;

    // Function to swap diagonal of matrix
    static void swapDiagonal(int [,]matrix) {
        for (int i = 0; i < N; i++) {
        int temp = matrix[i,i];
        matrix[i,i] = matrix[i,N - i - 1];
        matrix[i,N - i - 1] = temp;
        }
    }

    // Driver function
    public static void Main() {
        int [,]matrix = {{0, 1, 2},
                         {3, 4, 5},
                         {6, 7, 8}};

        swapDiagonal(matrix);

        // Displaying modified matrix
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < N; j++)
                Console.Write(matrix[i,j] + " ");
            Console.WriteLine();
        }
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP Program to swap
// diagonal of a matrix

// size of square matrix
$N = 3;

// Function to swap
// diagonal of matrix
function swapDiagonal($matrix)
{
    global $N;
    for ($i = 0; $i < $N; $i++)
    {
        $tmp=$matrix[$i][$i];
        $matrix[$i][$i] = $matrix[$i][$N - $i - 1];
        $matrix[$i][$N - $i - 1] = $tmp;
    }

// Displaying modified matrix
for ($i = 0; $i < $N; $i++)
{
    for ($j = 0; $j < $N; $j++)
        echo $matrix[$i][$j] . " ";
    echo "\n";
}
}

// Driver Code
$matrix = array(array(0, 1, 2),
                array(3, 4, 5),
                array(6, 7, 8));

swapDiagonal($matrix);

// This code is contributed by mits
?>

Javascript

<script>

// JavaScript program to swap
// diagonal of a matrix.

// size of square matrix
let N = 3;

// Function to swap diagonal of matrix
function swapDiagonal(matrix) {
    for (let i = 0; i < N; i++) {
    let temp = matrix[i][i];
    matrix[i][i] = matrix[i][N - i - 1];
    matrix[i][N - i - 1] = temp;
    }
}


// Driver code

    let matrix = [[0, 1, 2],
                      [3, 4, 5],
                      [6, 7, 8]];

    swapDiagonal(matrix);

    // Displaying modified matrix
    for (let i = 0; i < N; i++) {
    for (let j = 0; j < N; j++)
        document.write(matrix[i][j] + " ");
    document.write("<br/>");
    }

</script>

Output

2 1 0 
3 4 5 
8 7 6 

Time Complexity: O(N*N), as we are using nested loops to traverse N*N times.
Auxiliary Space: O(1), as we are not using any extra space.