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?
public class RotateImage { //先旋转最外面一层，再旋转里面的层 注意：四个角的不应该重复旋转，故应该最大为n-2 public void rotate(int[][] matrix) { if(matrix==null || matrix.length<2) return; int n = matrix.length; for(int i=0;i<n-1;i++) { for(int j=i;j<n-1-i;j++) { //旋转90度，横坐标变为纵坐标 int tmp = matrix[i][j]; matrix[i][j] = matrix[n-1-j][i]; matrix[n-1-j][i] = matrix[n-1-i][n-1-j]; matrix[n-1-i][n-1-j] = matrix[j][n-1-i]; matrix[j][n-1-i] = tmp; } } } //比较容易理解的做法 //先对角线进行交换，然后第一列和最后一列交换，第二列和倒数第二列交换 public void rotate2(int[][] matrix) { if(matrix==null || matrix.length<2) return; int n = matrix.length; //对角线交换 for(int i=0;i<n;i++) { for(int j=i;j<n;j++) { int temp = 0; temp = matrix[i][j]; matrix[i][j] = matrix[j][i]; matrix[j][i] = temp; } } //列列交换 for(int i =0 ; i<n; i++){ for(int j = 0; j<n/2; j++){ int temp = 0; temp = matrix[i][j]; matrix[i][j] = matrix[i][matrix.length-1-j]; matrix[i][matrix.length-1-j] = temp; } } } }