leetcode 48. Rotate Image

Seawolf

1. 
   
2. You are given an n x n 2D matrix representing an image.
   
3. 
   
4. Rotate the image by 90 degrees (clockwise).
   
5. 
   
6. Note:
   
7. 
   
8. 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.
   
9. 
   
10. Example 1:
    
11. 
    
12. Given input matrix =
    
13. [
    
14.   [1,2,3],
    
15.   [4,5,6],
    
16.   [7,8,9]
    
17. ],
    
18. 
    
19. rotate the input matrix in-place such that it becomes:
    
20. [
    
21.   [7,4,1],
    
22.   [8,5,2],
    
23.   [9,6,3]
    
24. ]
    
25. Example 2:
    
26. 
    
27. Given input matrix =
    
28. [
    
29.   [ 5, 1, 9,11],
    
30.   [ 2, 4, 8,10],
    
31.   [13, 3, 6, 7],
    
32.   [15,14,12,16]
    
33. ],
    
34. 
    
35. rotate the input matrix in-place such that it becomes:
    
36. [
    
37.   [15,13, 2, 5],
    
38.   [14, 3, 4, 1],
    
39.   [12, 6, 8, 9],
    
40.   [16, 7,10,11]
    
41. ]

复制代码

1. class Solution {
   
2.     public void rotate(int[][] matrix) {
   
3.         if(matrix.length == 0) return;
   
4.         int row = matrix.length -1;
   
5.         int col = matrix[0].length -1;
   
6.         int repeat = 0;
   
7.         for(int i = 0 ; i <= row/2; i++){
   
8.             
   
9.             for(int j = 0 ; j <= col /2 ; j++){
   
10.                
    
11.                 if(row % 2 == 0 && i == row/2 && j != col/2) continue;
    
12.                 swap(matrix, i ,j);
    
13.                
    
14.             }
    
15.         }
    
16.     }
    
17.    
    
18.     public void swap(int[][] matrix, int i, int j){
    
19.         int row = matrix.length - 1;
    
20.         int col = matrix[0].length - 1;
    
21.         
    
22.         int temp = matrix[i][j];
    
23.         matrix[i][j] = matrix[row - j][i];
    
24.         matrix[row- j][i] = matrix[row-i][col - j];
    
25.         matrix[row- i][col - j] = matrix[j][col - i];
    
26.         matrix[j][col- i] = temp;
    
27.         
    
28.     }
    
29.    
    
30. }

复制代码