package amazon;

// You are given an n x n 2D matrix representing an image.

// Rotate the image by 90 degrees (clockwise).

// Follow up:

// Could you do this in-place?

/**

* 旋转图像

* <p>

* 1 2 3 1 4 7 7 4 1

* 4 5 6 ----正对角线翻转---> 2 5 8 ----竖对角线翻转---> 8 5 2

* 7 8 9 3 6 9 9 6 3

* Created by anduo on 17-3-13.

*/

public class RotateImage {

public void rotate(int[][] matrix) {

if (matrix == null || matrix.length == 0) {

return;

}

int rows = matrix.length;

int cols = matrix[0].length;

// 正对角线翻转

for (int i = 0; i < rows; i++) {

for (int j = 0; j < i; j++) {

// swap

// a ^= b; b ^= a; a ^= b;

matrix[i][j] ^= matrix[j][i];

matrix[j][i] ^= matrix[i][j];

matrix[i][j] ^= matrix[j][i];

}

}

// 竖对角线翻转

for (int i = 0; i < rows; i++) {

for (int j = 0; j < cols / 2; j++) {

matrix[i][j] ^= matrix[i][cols - j - 1];

matrix[i][cols - j - 1] ^= matrix[i][j];

matrix[i][j] ^= matrix[i][cols - j - 1];

}

}

}

}