LeetCode 48 Rotate Image

原题:（频率2）

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 in-place, 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]
]

题意：向右旋转90°

代码和思路：

class Solution {
public void rotate(int[][] matrix) {
//先向左90度转，把横排转换为竖排
for(int i=0;i<matrix.length;i++){
for(int j = i;j<matrix[0].length;j++){
int temp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = temp;
}
}
//然后将竖排交换（第一竖排换最后竖排，第二换倒数第二）
for(int i=0;i<matrix.length;i++){
for(int j = 0;j<matrix.length/2;j++){
int temp = matrix[i][j];
matrix[i][j] = matrix[i][matrix.length-1-j];
matrix[i][matrix.length-1-j] = temp;
}
}
}
}