LeetCodeOnlineJudge题目C#练习-SparialMatrixII

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Given an integer n, generate a square matrix filled with elements from 1 to n2(Square(n)) in spiral order.
For example,
Given n = 3,

You should return the following matrix:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

 1         public static List<List<int>> SparialMatrixII(int n)
 2         {
 3             List<List<int>> ret = new List<List<int>>();
 4             if (n == 0)
 5                 return ret;
 6             if (n == 1)
 7             {
 8                 ret.Add(new List<int> { 1 });
 9                 return ret;
10             }
11 
12             for (int i = 1; i <= n; i++)
13             {
14                 ret.Add(new List<int>(n));
15             }
16 
17             int num = 1;
18 
19             for (int i = 0; i <= n / 2; i++)
20             {
21                 for (int col = i; col <= n - 1 - i; col++)
22                     ret[i][col] = num++;
23                 for (int row = i + 1; row <= n - 1 - i; row++)
24                     ret[row][n - 1 - i] = num++;
25                 for (int col = n - 1 - i - 1; col >= i; col--)
26                     ret[n - 1 - i][col] = num++;
27                 for (int row = n - 1 - i - 1; row >= i + 1; row--)
28                     ret[row][i] = num++;
29             }
30 
31             return ret;
32         }