Leetcode: Spiral Matrix

Given a matrix of m x 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].

 1 public class Solution {
 2     public List<Integer> spiralOrder(int[][] matrix) {
 3         ArrayList<Integer> res = new ArrayList<Integer>();
 4         if (matrix==null || matrix.length==0 || matrix[0].length==0) return res;
 5         int Min = Math.min(matrix.length, matrix[0].length);
 6         int levelMax = Min / 2;
 7         for (int level=0; level<levelMax; level++) {
 8             for (int i=level; i<matrix[0].length-1-level; i++) {
 9                 res.add(matrix[level][i]);
10             }
11             for (int i=level; i<matrix.length-1-level; i++) {
12                 res.add(matrix[i][matrix[0].length-1-level]);
13             }
14             for (int i=matrix[0].length-1-level; i>level; i--) {
15                 res.add(matrix[matrix.length-1-level][i]);
16             }
17             for (int i=matrix.length-1-level; i>level; i--) {
18                 res.add(matrix[i][level]);
19             }
20         }
21         if (Min % 2 == 1) {
22             if (matrix.length < matrix[0].length) {
23                 for (int i=levelMax; i<matrix[0].length-levelMax; i++) {
24                     res.add(matrix[levelMax][i]);
25                 }
26             }
27             else {
28                 for (int i=levelMax; i<matrix.length-levelMax; i++) {
29                     res.add(matrix[i][levelMax]);
30                 }
31             }
32         }
33         return res;
34     }
35 }