Spiral Matrix

题目：

Given a matrix of m ✕ n elements (m rows, n columns), return all elements of the
matrix in spiral order.
For example, given the following matrix:
[
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5]

解答：

 1 public class Solution {
 2     public static void main(String[] args) {
 3         int[][] matrix = {{1,2,3},{4,5,6},{7,8,9}};
 4         List<Integer> elements = spiralOrder(matrix);
 5     }
 6 
 7     public List<Integer> spiralOrder(int[][] matrix) {
 8         List<Integer> elements = new ArrayList<>();
 9 
10         if(matrix.length == 0) {
11             return elements;
12         }
13 
14         int m = matrix.length;
15         int n = matrix[0].length;
16         int row = 0;
17         int col = -1;
18 
19         while(true) {
20             for(int i = 0; i < n; i++) {
21                 elements.add(matrix[row][++col]);
22             }
23 
24             if(--m == 0) {
25                 break;
26             }
27 
28             for(int i = 0; i < m; i++) {
29                 elements.add(matrix[++row][col]);
30             }
31 
32             if(--n == 0) {
33                 break;
34             }
35 
36             for(int i = 0; i < n; i++) {
37                 elements.add(matrix[row][--col]);
38             }
39 
40             if(--m == 0) {
41                 break;
42             }
43 
44             for(int i = 0; i < m; i++) {
45                 elements.add(matrix[--row][col]);
46             }
47 
48             if(--n == 0) {
49                 break;
50             }
51         }
52 
53         return elements;
54     }
55 }