Spiral Matrix II

注意边界
 1 public class Solution {
 2     public int[][] generateMatrix(int n) {
 3         // IMPORTANT: Please reset any member data you declared, as
 4         // the same Solution instance will be reused for each test case.
 5         if(n <= 0)
 6             return new int[0][];
 7         int[][] matrix = new int[n][n];
 8         printCircle(matrix, 0, n, 1);
 9         return matrix;
10     }
11     private void printCircle(int[][] matrix, int start, int end, int n)
12     {
13         if(start >= end)
14             return;
15         if(end - start == 1){
16             matrix[start][start] = n;
17             return;
18         }
19         for(int i = start; i < end - 1; i++)
20         {
21             matrix[start][i] = n;
22             n++;
23         }
24         for(int i = start; i < end - 1; i++)
25         {
26             matrix[i][end - 1] = n;
27             n++;
28         }
29         for(int i = end - 1; i > start; i--)
30         {
31             matrix[end - 1][i] = n;
32             n++;
33         }
34         for(int i = end - 1; i > start; i--)
35         {
36             matrix[i][start] = n;
37             n++;
38         }
39         printCircle(matrix, start+1, end-1, n);
40     }
41 }