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]
]
这题就相当于找规律。。
规律:将第一行和最后一行交换，第二行和倒数第二行交换，。。。然后将关于对角线对称的元素交换。
代码如下：注意二维数组的长度表示。
class Solution {
public void rotate(int[][] matrix) {
//第一步：将第一行和最后一行交换，第二行和倒数第二行交换。。
for(int i=0;i<matrix.length/2;i++)
for(int j=0;j<matrix[0].length;j++){
int tmp=matrix[i][j];
matrix[i][j]=matrix[matrix.length-1-i][j];
matrix[matrix.length-1-i][j]=tmp;
}
//第二步：交换关于对角线对称的元素
for(int i=0;i<matrix.length;i++)
for(int j=i+1;j<matrix[0].length;j++){
int tem=matrix[i][j];
matrix[i][j]=matrix[j][i];
matrix[j][i]=tem;
}
}
}