C Program for Program to Interchange Diagonals of Matrix

Write a C program for a given square matrix of order n*n, the task is to interchange the elements of both diagonals. 

Examples :

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

Input : matrix[][] = {4, 2, 3, 1,
5, 7, 6, 8,
9, 11, 10, 12,
16, 14, 15, 13}
Output : matrix[][] = {1, 2, 3, 4,
5, 6, 7, 8,
9, 10, 11, 12,
11, 14, 15, 16}

Approach:

Idea behind interchanging diagonals of a square matrix is simple. Iterate from 0 to n-1 and for each iteration you have to swap a[i][i] and a[i][n-i-1]. 

Below in the implementation of the above approach:

C

// C program of the above approach
#include <stdio.h>

#define N 3

// Function to interchange diagonals
void interchangeDiagonals(int array[N][N])
{
    // Swap elements of diagonal
    for (int i = 0; i < N; ++i)
        if (i != N / 2) {
            int temp = array[i][i];
            array[i][i] = array[i][N - i - 1];
            array[i][N - i - 1] = temp;
        }

    for (int i = 0; i < N; ++i) {
        for (int j = 0; j < N; ++j)
            printf(" %d", array[i][j]);
        printf("\n");
    }
}

// drivers Code
int main()
{
    int array[N][N]
        = { { 4, 5, 6 }, { 1, 2, 3 }, { 7, 8, 9 } };
    interchangeDiagonals(array);
    return 0;
}

Output

 6 5 4
 1 2 3
 9 8 7

Time Complexity: O(N*N), as we are using nested loops for traversing the matrix.
Auxiliary Space: O(1), as we are not using any extra space.

Please refer complete article on Program to Interchange Diagonals of Matrix for more details!