Rotate Image

题目要求：

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.

翻转一个二维数组90度。（数组大小为N*N）

例如，输入：

matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
]

输出：

[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]

输入：

matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
]

输出：

[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

思路：

 

如图，数组翻转90度，只需要以蓝色三角内，每个数字为基准，进行旋转，以一个数字为基准，移动4次，即上图中4个箭头的指向。

代码如下：

class Solution {
    public void rotate(int[][] matrix) {
      int matrixLength=matrix.length;

        for (int i = 0; i < matrixLength/2; i++) {
            for (int j = i; j <matrixLength-i-1 ; j++) {
                int tmpValue1=matrix[i][j];

                matrix[i][j]=matrix[matrixLength-1-j][i];
                matrix[matrixLength-1-j][i]=matrix[matrixLength-1-i][matrixLength-1-j];
                matrix[matrixLength-1-i][matrixLength-1-j]=matrix[j][matrixLength-1-i];
                matrix[j][matrixLength-1-i]=tmpValue1;
            }
        }
    }
}

结果：