leetcode-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]
]

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