Rotating 2d array clockwise

Question

i need to create ad 2d dynamic array and then create a function that will receive the 2d dynamic array and then rotate it 90 degrees clockwise and return it back to main. However i am not sure why i am not getting any output? is it because of the wrong swapping technique? i figured that the indices swapping is as follows:

I J-----------I J
0 0           0 1
0 1           1 1
0 2           2 1

with that i came with :

for (int i = 0; i <row;i++)

    for(int j = 0;j<col; j++)
    {
        Roti[i+j][row-i]=arr[i][j];

    }

Code:

#include <iostream>
using namespace std;
void print2DArray(int **arr, int rows, int cols);
int **Rotate(int **arr, int row, int col)
{
    int **Roti = new int *[row];

    for (int i = 0; i <row;i++)
    {
        Roti[i] = new int [col];
    }


    for (int i = 0; i <row;i++)

        for(int j = 0;j<col; j++)
        {
            Roti[i+j][row-i]=arr[i][j];

        }
    return  Roti;
}

int main()
{
    int *A[3];
    for (int i = 0; i < 3; i++)
    {
        A[i] = new int[3];
        for (int j = 0; j < 3; j++)
        {
            A[i][j] = rand() % 20;
        }
    }
    cout << "The array is :\n";
    print2DArray(A, 3, 3);
    int **ptr;
    ptr=Rotate(A,3,3);
cout<<"-----"<<endl;
    print2DArray(ptr, 3, 3);




    for (int i = 0; i < 3; i++)
    {
        delete[] A[i];
    }
    return 0;
}
void print2DArray(int **arr, int rows, int cols)
{
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < cols; j++)
        {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }

}

Answer 1

Hopefully by "rotation" you did not mean the regular transpose because there are many answers for that already on stackoverflow. What is the fastest way to transpose a matrix in C++?

For rotation of the matrix, I modified your code to make it work as shown below. The logic is simply that the first row of the original matrix becomes the last column of the rotated matrix and using this logic, you come up with the the following code. Hope it helps.

#include <iostream>
using namespace std;

void print2DArray(int **arr, int rows, int cols);
int **Rotate(int **arr, int num_rows, int num_cols);

int main()
{
    int num_rows = 3;
    int num_cols = 3;
    int** A_matrix = new int*[num_rows];
    for (int i = 0; i < num_rows; i++)
        A_matrix[i] = new int[num_cols];

    for (int row = 0; row < num_rows; row++)
    {
        for (int col = 0; col < num_cols; col++)
        {
            A_matrix[row][col] = rand() % 20;
        }
    }

    cout << "The array is :\n";
    print2DArray(A_matrix, 3, 3);

    int** roated_matrix;
    roated_matrix = Rotate(A_matrix, num_rows, num_cols);
    cout << "Rotated array:" << endl;
    print2DArray(roated_matrix, 3, 3);


    return 0;
}

int **Rotate(int **arr, int num_rows, int num_cols)
{
    /* Rotated matrix will have dimensions reverse as well. 
       That's why we have rows and cols reversed in the following lines */
    int** rotated_matrix = new int*[num_cols];
    for (int i = 0; i < num_cols; i++)
        rotated_matrix[i] = new int[num_rows];


    for (int row = 0; row < num_rows; row++)
    {
        int col_rotated_matrix = num_rows - 1 - row; // 1st row shall be copied to the last column and so on
        for (int col = 0; col < num_cols; col++)
        {
            int row_rotated_matrix = col; // rows become columns in the rotated matrix
            rotated_matrix[row_rotated_matrix][col_rotated_matrix] = arr[row][col];
        }
    }
    return rotated_matrix;
}
void print2DArray(int **arr, int rows, int cols)
{
    for (int i = 0; i < rows; i++)
    {
        for (int j = 0; j < cols; j++)
        {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
}

It produces the following output:

The array is :
1 7 14
0 9 4
18 18 2
Rotated array:
18 0 1
18 9 7
2 4 14

Answer 2

Try Using this;

for (int i = 0; i <row;i++)
k = row.length -1 ;
    for(int j = 0;j<col; j++)
    {
        Roti[j][k]=arr[i][j];

    }
}