48. Rotate Image

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:

Giveninput matrix =

[

  [1,2,3],

  [4,5,6],

  [7,8,9]

],

rotate the input matrixin-placesuch that it becomes:

[

  [7,4,1],

  [8,5,2],

  [9,6,3]

]

Example 2:

Giveninput matrix =

[

  [ 5, 1, 9,11],

  [ 2, 4, 8,10],

  [13, 3, 6, 7],

  [15,14,12,16]

],

rotate the input matrixin-placesuch that it becomes:

[

  [15,13, 2, 5],

  [14, 3, 4, 1],

  [12, 6, 8, 9],

  [16, 7,10,11]

]

自己想到的太过复杂 从外层向里 最外层走n-1步...

这题如果真没做过 挺难想的

原输入

1  2  3
4  5  6
7  8  9

先1，5，9为界限 对角翻转 翻转后

1  4  7
2  5  8
3  6  9

以中间行为界限 上下交换

7  4  1
8  5  2
9  6  3

public class Solution {
    public void rotate(int[][] matrix) {
        for(int i = 0; i<matrix.length; i++){
            for(int j = i; j<matrix[0].length; j++){
                int temp = 0;
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
        for(int i =0 ; i<matrix.length; i++){
            for(int j = 0; j<matrix.length/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;
            }
        }
    }
}

以后对于这种reverse的题目 多想想怎样分成两步实现