C Program to Rotate Matrix Elements

Here, we will build a C Program to rotate matrix elements with an approach to ring/rotate elements independently.

Input:

1  2  3
4  5  6
7  8  9

Output:

4  1  2  
7  5  3
8  9  6

Approach

We rotate all rings of elements one by one, This process is starting from the outermost ring, and then follows the same step for the inner ring. To rotate a ring, we need to do the following steps. 

1. Move elements of the top row. 
2. Move elements of the last column. 
3. Move elements of the bottom row. 
4. Move elements of the first column. 
5. Repeat the above steps for the inner ring while there is an inner ring.

Example:

C

// C program to demonstrate
// rotation of a matrix elements
#include <stdio.h>

#define R 4 // macros
#define C 4 // macros

// function to rotate a matrix mat[][] of size m x n.
// m = Row and n = Column
void rotatematrix(int m, int n, int mat[R][C])
{
    int row = 0, col = 0;
    int prev, curr;
    /*
    row: Starting row index
    m: ending row index
    col: starting column index
    n: ending column index
    i: iterator
    */

    while (row < m && col < n) {

        if (row + 1 == m || col + 1 == n)
            break;

        // Store the first element of next row and this
        // element will replace the first element of current
        // row
        prev = mat[row + 1][col];

        // Move elements of first row from remaining rows
        for (int i = col; i < n; i++) {
            curr = mat[row][i];
            mat[row][i] = prev;
            prev = curr;
        }
        row++;

        // Move the elements of last column from the
        // remaining columns
        for (int i = row; i < m; i++) {
            curr = mat[i][n - 1];
            mat[i][n - 1] = prev;
            prev = curr;
        }
        n--;

        // Move the elements of last row from the remaining
        // rows
        if (row < m) {
            for (int i = n - 1; i >= col; i--) {
                curr = mat[m - 1][i];
                mat[m - 1][i] = prev;
                prev = curr;
            }
        }
        m--;

        // Move the elements of first column from the
        // remaining rows
        if (col < n) {
            for (int i = m - 1; i >= row; i--) {
                curr = mat[i][col];
                mat[i][col] = prev;
                prev = curr;
            }
        }
        col++;
    }
}

// Driver code
int main()
{
    // create a matrix of size RxC
    // R - Rows, C - Columns
    int mat[R][C] = { { 1, 2, 3, 4 },
                      { 5, 6, 7, 8 },
                      { 9, 10, 11, 12 },
                      { 13, 14, 15, 16 } };

    // Print input matrix
    printf("\n Input Matrix \n");
    for (int i = 0; i < R; i++) {
        for (int j = 0; j < C; j++) {
            printf(" %d ", mat[i][j]);
        }
        printf("\n");
    }

    // This function is rotate the elements of matrix.
    rotatematrix(R, C, mat);

    // Print rotated matrix
    printf("\n Rotated Matrix \n");
    for (int i = 0; i < R; i++) {
        for (int j = 0; j < C; j++) {
            printf(" %d ", mat[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Output

 Input Matrix 
 1  2  3  4 
 5  6  7  8 
 9  10  11  12 
 13  14  15  16 

 Rotated Matrix 
 5  1  2  3 
 9  10  6  4 
 13  11  7  8 
 14  15  16  12 

Time Complexity: O(m*n), where m is the number of rows and n is the number of columns.
Auxiliary Space: O(1), No extra Space is used.