题目描述:
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] ]
中文理解:
给定一个二维数组,返回二维数组顺时针旋转90°后的表示,原地进行,不占用其他额外的空间。
解题思路:
首先将数组按照纵向中轴旋转,然后再以反向对角线来进行旋转即可完成原地顺时针旋转90°。
代码(java):
class Solution {
public void rotate(int[][] matrix) {
//先按照中轴对称转换,再按照反向对角线转换
int row=matrix.length;
if(row==0)return;
int temp=0;
//按照中轴对阵转换
for(int i=0;i<row;i++){
for(int j=0;j<row/2;j++){
temp=matrix[i][j];
matrix[i][j]=matrix[i][row-j-1];
matrix[i][row-j-1]=temp;
}
}
//按照反向对角线转换
for(int i=0;i<row;i++){
for(int j=0;j<row-i;j++){
temp=matrix[i][j];
matrix[i][j]=matrix[row-1-j][row-1-i];
matrix[row-1-j][row-1-i]=temp;
}
}
return;
}
}