LeetCode 59. Spiral Matrix II

原题链接在这里：https://leetcode.com/problems/spiral-matrix-ii/

题目：

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 ]
]

题解：

从外圈到内圈螺旋着填数，如果n是奇数的话，最后正中间的数需要单独填写.

Time Complexity: O(n^2). Space: O(n^2).

AC Java:

 1 class Solution {
 2     public int[][] generateMatrix(int n) {
 3         int [][] res = new int[n][n];
 4         int num = 1;
 5         int x = 0; 
 6         int y = 0;
 7         
 8         //由外到内，旋转加值
 9         while(n>1){
10             for(int j = 0; j){
11                 res[x][y++] = num++;
12             }
13             
14             for(int i = 0; i){
15                 res[x++][y] = num++;
16             }
17             
18             for(int j = 0; j){
19                 res[x][y--] = num++;
20             }
21             
22             for(int i = 0; i){
23                 res[x--][y] = num++;
24             }
25             
26             n-=2;
27             x++;
28             y++;
29         }
30         
31         if(n%2 == 1){
32             res[x][y] = num;
33         }
34         
35         return res;
36     }
37 }

类似Spiral Matrix. 

跟上Spiral Matrix III.