Rotate Matrix Elements

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Given a matrix, clockwise rotate elements in it.

Examples:

Input
1    2    3
4    5    6
7    8    9

Output:
4    1    2
7    5    3
8    9    6

For 4*4 matrix
Input:
1    2    3    4    
5    6    7    8
9    10   11   12
13   14   15   16

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

The idea is to use loops similar to the program for printing a matrix in spiral form. One by one rotate all rings of elements, starting from the outermost. To rotate a ring, we need to do following.
1) Move elements of top row.
2) Move elements of last column.
3) Move elements of bottom row.
4) Move elements of first column.
Repeat above steps for inner ring while there is an inner ring.

// C++ program to rotate a matrix
#include <bits/stdc++.h>
#define R 4
#define C 4
using namespace std;
// A function to rotate a matrix mat[][] of size R x C.
// Initially, m = R and n = C
void rotatematrix(int m, int n, int mat[R][C])
{
    int row = 0, col = 0;
    int prev, curr;
    /*
       row - Staring 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, this
        // element will replace first element of current
        // row
        prev = mat[row + 1][col];
         /* Move elements of first row from the remaining rows */
        for (int i = col; i < n; i++)
        {
            curr = mat[row][i];
            mat[row][i] = prev;
            prev = curr;
        }
        row++;
        /* Move 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 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 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++;
    }
    // Print rotated matrix
    for (int i=0; i<R; i++)
    {
        for (int j=0; j<C; j++)
          cout << mat[i][j] << " ";
        cout << endl;
    }
}
/* Driver program to test above functions */
int main()
{
    // Test Case 1
    int a[R][C] = { {1,  2,  3,  4},
        {5,  6,  7,  8},
        {9,  10, 11, 12},
        {13, 14, 15, 16}  };
    // Tese Case 2
    /* int a[R][C] = {{1, 2, 3},
                      {4, 5, 6},
                      {7, 8, 9}
                     };
     */  rotatematrix(R, C, a);
    return 0;
}

Output:

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

Disclaimer: This content belongs to geeksforgeeks, source: http://geeksforgeeks.org

rakesh

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