leetcode -- Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n² in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

java 中是传值的，将count作为返回值返回

 1 public static int[][] generateMatrix(int n) {
 2         // Start typing your Java solution below
 3         // DO NOT write main() function
 4         if(n <= 0)
 5             return new int[0][];
 6         
 7         int rows = n;
 8         int cols = n;
 9         int[][] result = new int[n][n];
10         int count = 1;
11         
12         int start = 0;
13         while (rows > start * 2 && cols > start * 2) {
14             count = printCircle(result, rows, cols, start, count, n * n);
15             start++;
16         }
17         
18         return result;
19     }
20     
21     public static int printCircle(int[][] matrix, int rows, int cols,
22             int start, int count, int n) {
23         int endX = cols - 1 - start;
24         int endY = rows - 1 - start;
25 
26         // print row
27         for (int i = start; i <= endX && count <= n; i++) {
28             matrix[start][i] = count ++;
29         }
30 
31         // print col
32         if (endY > start) {
33             for (int i = start + 1; i <= endY && count <= n; i++) {
34                 matrix[i][endX] = count ++;
35             }
36         }
37         // print row
38         if (endX > start && endY > start) {
39             for (int i = endX - 1; i >= start && count <= n; i--) {
40                 matrix[endY][i] = count ++;
41             }
42         }
43         // print col
44         if (endX > start && endY - 1 > start) {
45             for (int i = endY - 1; i > start && count <= n; i--) {
46                 matrix[i][start] = count ++;
47             }
48         }
49         return count;
50     }