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:

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]
]
将N*N的矩阵，顺时针旋转90度

例如：  
1  2  3         7  8  9       7  4  1

4  5  6    =》  4  5  6  =》   8  5  2

7  8  9         1  2  3       9  6  3

 public void swapUpDown(int[][] matrix, int rowUp,int rowDown) {
        if(matrix.length == 0) return;
        for (int i = 0; i < matrix[0].length; i++) {
            int temp = matrix[rowUp][i];
            matrix[rowUp][i] = matrix[rowDown][i];
            matrix[rowDown][i]= temp;
        }
    }

    public void swapLeftRight(int[][] matrix, int colLeft,int colRight) {
        for (int i = 0; i < matrix.length; i++) {
            int temp = matrix[i][colLeft];
            matrix[i][colLeft] = matrix[i][colRight];
            matrix[i][colRight] = temp;
        }
    }
    
    public void rotate(int[][] matrix) {
        int length = matrix.length;
        if (length < 2) return;
//        顺时针:上下互换  逆时针：左右互换
        int mid = matrix.length / 2;
        for (int col = 0; col < mid; col++) {
            if (length % 2 == 0) {
                swapUpDown(matrix, col,mid * 2 - col - 1);
            } else {
                swapUpDown(matrix, col,mid * 2 - col);
            }
        }
           //沿着左上到右下的对角线，交换对称的节点
        for (int i = 0; i < matrix.length; i++) {
            for (int j = i + 1; j < matrix[i].length; j++) {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        } 
    }