48. Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

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:

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

Example 2:

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

 

Constraints:

//先让矩阵对称，然后水平轴对称

1 2 3  变成 1 4 7 变成 7 4 1

4 5 6        2 5 8        8 5 2
7 8 9        3 6 9        9 6 3

 

 

public void rotate(int[][] matrix) {
  for(int i=0;i<matrix.length;i++){
    for(int j=i;j<matrix[0].length;j++){
      int 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[0].length/2;j++){
      int temp=matrix[i][j];
      matrix[i][j]=matrix[i][matrix[0].length-1-j];
      matrix[i][matrix[0].length-1-j]=temp;
    }
  }
}