Difficulty: Medium
You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
You have to rotate the image , which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Given input matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
rotate the input matrix in-place such that it becomes:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
Example 2:
Given input matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
rotate the input matrix in-place such that it becomes:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
Language: Java
class Solution { // 解决这个问题的关键就是知道，图像旋转90度是可以通过先对称镜像，然后对角线镜像可以得到旋转结果
public void rotate(int[][] matrix) {
// 首先垂直镜像反转
for (int j = 0; j < matrix.length / 2; j++) {
for (int i = 0; i < matrix.length; i++) {
int tmp = matrix[j][i];
matrix[j][i] = matrix[matrix.length - 1 - j][i];
matrix[matrix.length - 1 - j][i] = tmp;
}
}
// 然后按照对角线反转
for (int i = 0; i < matrix.length; i++) {
for (int j = i + 1; j < matrix.length; j++) {
int tmp = matrix[j][i];
matrix[j][i] = matrix[i][j];
matrix[i][j] = tmp;
}
}
}
}