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]
]

代码如下

public class RotateImage {

	public static void main(String[] args) {
		int[][] matrix = new int[][]{{1,2,3},{4,5,6},{7,8,9}};
		rotate2(matrix);
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[i].length; j++) {
				System.out.print(matrix[i][j]+",");
			}
			System.out.println();
		}
	}
	
    public static void rotate(int[][] matrix) {    	
    	int n = matrix.length;
    	int[][] temp = new int[n][n];
    	
    	for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				temp[j][n-1-i] = matrix[i][j];
			}
		}
    	
    	for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				matrix[i][j] = temp[i][j];
			}
		}
    }
    
    public static void rotate2(int[][] matrix) {    	
    	int n = matrix.length;
    	for (int i = 0; i < n/2; i++) {
			for (int j = i; j < n-1-i; j++) {
				int temp = 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] = temp;
			}
		}
    }
    
    public static void rotate3(int[][] matrix) {    	
    	int n = matrix.length;
    	int[][] temp = new int[n][n];
    	
    	for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				temp[i][j] = matrix[n-1-j][i];
			}
		}
    	
    	for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				matrix[i][j] = temp[i][j];
			}
		}
    } 

}