CareerCup1.6.cpp

CareerCup1.6.cpp

/* Chapter 1
 * 1.6 Given an image represented by an N*N matrix, where each pixel in the image is 4 bytes,
 * write a method to rotate the image by 90 degrees. Can you do this in place?
 */

/* Rotate 90 degree counter-clockwise */

#include <iostream>

using namespace std;

#define N 4

// Rotate by Swap
void rotate1(int matrix[][N])
{
    int layer = N/2;  // top_left_right_bottom
    
    for (int i = 0; i < layer; ++i)
    {
        int begin = i; // iteration begin index
        int end = N - 1 - i;  // iteration end index
        
        for (int j = begin; j < end; j++)
        {
            // About the subscripts, you have to induct from small examples
            // save top
            int top = matrix[i][j];
            // right -> top
            matrix[i][j] = matrix[j][end];
            // bottom -> right
            matrix[j][end] = matrix[end][end - j + begin];
            // left -> bottom
            matrix[end][end - j + begin] = matrix[end - j + begin][begin];
            // top -> left
            matrix[end - j + begin][begin] = top;
        }
    }
    
}

/* Rotate 90 degree clockwise */
// Rotate by Flip
void rotate2(int matrix[][N])
{
    // diagonal flip
    for (int i = 0; i < N; ++i)
    {
        for (int j = 0; j < N; ++j)
        {
            if (i < j)
            {
                int tmp = matrix[i][j];   // save upper right tri-angle area
                matrix[i][j] = matrix[j][i];  // assign lower left to upper right tri-angle area
                matrix[j][i] = tmp;   // assign upper right to lower left tri-angle area
            }
        }
    }
    // vertical middle line flip
    for (int j = 0; j < N/2; ++j)
    {
        for (int i = 0; i < N; ++i)
        {
            int tmp = matrix[i][j];    // save left
            matrix[i][j] = matrix[i][N - j - 1];   // assign right to left
            matrix[i][N - j - 1] = tmp;   // assign left to right
        }
    }
    
    
}

// Main
int main(int argc, char const *argv[])
{
    int matrix [N][N] = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}};
//    int matrix [N][N] = {{1, 2}, {3, 4}};
    rotate2(matrix);
    for (int i = 0; i < N; ++i) {
        for (int j = 0; j < N; ++j) {
            cout << matrix[i][j] << "   ";
            if (j == N - 1) {
                cout << endl;
            }
        }
    }
    return 0;
}