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 NOTallocate 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]
]

code参照cc189

class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length == 0 || matrix.length != matrix[0].length) return;
        
        
        int n = matrix.length;
        
        for(int layer = 0; layer < n / 2; layer++){
            int first = layer;
            int last = n - layer - 1;
            
            for(int i = first; i < last; i++){
                int offset = i - first;
                
                int top = matrix[first][i];
                //left -> top
                matrix[first][i] = matrix[last-offset][first];
                
                //bottom left;
                matrix[last-offset][first] = matrix[last][last-offset];
                
                //right bottom
                
                matrix[last][last - offset] = matrix[i][last];
                
                matrix[i][last] = top;
                
            }
            
        }
    }
}