You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Follow up:
Could you do this in-place?
In order to fulfill the follow up requirement, i.e. in-place, we should utilize a temporary int variable and switch the values in the matrix. Coming back to our problem, rotating a matrix can be divided into steps and each step responses to rotating specific layer of the matrix. For example, when n=6 there are n/2 = 3 steps from outside layers to inside layers.
public class Solution { /*public void rotate(int[][] matrix) { //本题一定要注意边界。每一层循环代表反转一层(从外到内循环),一共有len/2层。注意j的取值,j>=i,j<len-i-1; int len=matrix.length; for(int i=0;i<len/2;i++){ for(int j=i;j<len-i-1;j++){ int temp=matrix[i][j]; matrix[i][j]=matrix[len-1-j][i]; matrix[len-1-j][i]=matrix[len-1-i][len-1-j]; matrix[len-1-i][len-1-j]=matrix[j][len-i-1]; matrix[j][len-i-1]=temp; } } }*/ public void rotate(int[][] matrix) { //本题的另一种解法,首先沿着水平中线翻转一次,然后沿着主对角线,翻转一次,最终能够实现顺时针旋转90度 //或者,首先沿着副对角线翻转一次,然后沿着水平中线翻转一次。 int len=matrix.length; int i=0; int j=0; for(;i<len/2;i++){ for(j=0;j<len;j++){ int temp=matrix[i][j]; matrix[i][j]=matrix[len-1-i][j]; matrix[len-1-i][j]=temp; } } for(i=0;i<len;i++){ for(j=i+1;j<len;j++){ int temp=matrix[i][j]; matrix[i][j]=matrix[j][i]; matrix[j][i]=temp; } } } }
时间: 2024-11-04 23:55:02