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]
]

方法1：(就是一個普通的迴圈，要控制方向)

package leetcode;

import org.junit.Test;

/**
 * @author zhangyu
 * @version V1.0
 * @ClassName: RotateImage
 * @Description: TOTO
 * @date 2018/12/13 11:29
 **/


public class RotateImage {
    @Test
    public void fun() {
        int[][] matrix =
                {
                        {1, 2, 3},
                        {4, 5, 6},
                        {7, 8, 9}
                };
        rotate(matrix);
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public void rotate(int[][] matrix) {
        if (matrix == null || matrix.length < 1) {
            return;
        }

        // 先進行對稱交換
        for (int i = 0; i < matrix.length - 1; i++) {
            for (int j = i; j < matrix[0].length; j++) {
                swap(matrix, i, j, j, i);
            }
        }
       /*
        1  4  7
        2  5  8
        3  6  9*
        /

        // 再中間進行變換
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length / 2; j++) {
                swap(matrix, i, j, i, matrix[0].length - j - 1);
            }
        }
       /*
        7  4  1
        8  5  2
        9  6  3
        */
    }

    //陣列進行交換
    private void swap(int[][] nums, int x1, int y1, int x2, int y2) {
        int temp = nums[x1][y1];
        nums[x1][y1] = nums[x2][y2];
        nums[x2][y2] = temp;
    }
}
 

時間複雜度：O(n^2)

空間複雜度：O(1)