- There is a relation between the locations of exchanged
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
after rotation
13 9 5 1
14 10 6 2
15 11 7 3
16 12 8 4
(i, j) -> (j, n-1-i) -> (n-1-i, n-1-j) -> (n-1-j, i) -> (i, j)
- Swapping partial image is enough
- Carefully handle the size of image
5 6 7 8
9 10 11 12
13 14 15 16
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
C++ code :
#include <iostream>
using namespace std;
class Mat{
public:
Mat( const int *a, const int size );
~Mat();
void showElement() const;
void rotate( );
private:
int **m_image;
int m_size;
};
Mat::Mat( const int *a, const int size ) : m_image(NULL), m_size(size)
{
if( m_size <= 0 ) return;
m_image = new int*[m_size]( );
for( int i = 0 ; i < m_size ; i++ )
m_image[i] = new int[m_size]( );
// assign array value to member variable
for( int i = 0, p = 0 ; i < m_size ; i++ )
for( int j = 0 ; j < m_size ; j++ )
m_image[i][j] = a[p++];
}
Mat::~Mat(){
if(m_image){
for( int i = 0 ; i < m_size ; i++ )
delete [] m_image[i];
delete [] m_image;
}
}
void Mat::showElement() const{
for( int i = 0 ; i < m_size ; i++ ){
for ( int j = 0 ; j < m_size ; j++ )
cout << m_image[i][j] << " ";
cout << endl;
}
}
void Mat::rotate( ){
const int final_row = (m_size - 1) / 2;
const int final_col = (m_size % 2) ? (final_row - 1) : final_row;
const int final_index = m_size - 1;
// (i, j) -> (j, final_index-i) -> (final_index-i, final_index-j)
// -> (final_index-j, i) -> (i, j)
for( int i = 0 ; i <= final_row ; i++ ){
for( int j = 0 ; j <= final_col ; j++ )
{
int temp = m_image[final_index-j][i];
m_image[final_index-j][i] = m_image[final_index-i][final_index-j];
m_image[final_index-i][final_index-j] = m_image[j][final_index-i];
m_image[j][final_index-i] = m_image[i][j];
m_image[i][j] = temp;
}
}
}
int main( ){
const int SIZE = 4;
int image[SIZE * SIZE] = {1, 2, 3, 4,
5, 6, 7, 8,
9, 10,11,12,
13,14,15,16};
Mat mat( image, SIZE );
mat.showElement( );
mat.rotate( );
cout << endl;
mat.showElement( );
cout << endl;
const int SIZE2 = 5;
int image2[SIZE2 * SIZE2] = {1, 2, 3, 4, 5,
6, 7, 8, 9, 10,
11, 12, 13, 14, 15,
16, 17, 18, 19, 20,
21, 22, 23, 24, 25};
Mat mat2( image2, SIZE2 );
mat2.showElement( );
mat2.rotate( );
cout << endl;
mat2.showElement( );
return 0;
}
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