public class P0048RotateImage {

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

if(matrix.length == 0 )return;

int len = matrix.length;

//we need to retate the image by clockwise 90 degrees,we can transpose（转置）it into 2 steps: flip the matrix diagonal, and then flip it horizontally

for(int i = 0;i<len;i++){//N*N matrix

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

int temp = matrix[i][j];

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

matrix[j][i]=temp;

}

}

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

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

int temp = matrix[i][j];

matrix[i][j]=matrix[i][len-1-j];

matrix[i][len-1-j]=temp;

}

}

}

}

/*

旋转问题可以通过对角线，横向或者纵向轴翻转来获取结果。这道题目第一步是按照对角线翻转，第二步是水平翻转

1 2 3 1 4 7 7 4 1

4 5 6 ->对角线翻转 2 5 8 ->纵轴反转 8 5 2

7 8 9 3 6 9 9 6 3

例子2

5 1 9 11 5 2 13 15 15 13 2 5

2 4 8 10 1 4 3 14 14 3 4 1

13 3 6 7 9 8 6 12 12 6 8 9

15 14 12 16 11 10 7 16 16 7 10 11

*/