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]
]
 1 class Solution {
 2     public void transpose(int [][] matrix) {
 3         int n = matrix.length;
 4         for (int i = 0; i < n; ++i) {
 5             for (int j = i + 1; j < n; ++j) {
 6                 int temp = matrix[i][j];
 7                 matrix[i][j] = matrix[j][i];
 8                 matrix[j][i] = temp;
 9             }
10         }
11     }
12     
13     public void reverse(int []matrix) {
14         int n = matrix.length;
15         for (int i = 0, j = n - 1; i < j; i++, j--) {
16             int temp = matrix[i];
17             matrix[i] = matrix[j];
18             matrix[j] = temp;
19         }
20     }
21     public void rotate(int[][] matrix) {
22         transpose(matrix);
23         for (int i = 0; i < matrix.length; ++i) {
24             reverse(matrix[i]);
25         }
26     }
27 }

 

posted @ 2020-02-17 16:32  hyx1  阅读(127)  评论(0)  编辑  收藏  举报