【leetcode刷题笔记】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 ]

]

---

题解：以前做过的Spiral Matrix是给一个矩阵螺旋式的输出，这道题是给一个n，螺旋式的生成矩阵。和第一个的做法类似，定义四个变量

left:当前未填的子矩阵的最左边界

right:当前未填的子矩阵的最右边界

up:当前未填子矩阵的最上边界

down:当前未填子矩阵的最下边界

然后每次进行四个循环，做一个螺旋。

代码如下：

 1 public class Solution {

 2     public int[][] generateMatrix(int n) {

 3         int[][] matrix = new int[n][n];

 4         int left  = 0;

 5         int right = n-1;

 6         int up = 0;

 7         int down = n-1;

 8         int number = 0;

 9         while(number <= n*n-1){

10             for(int i = left;i <= right;i++){

11                 matrix[up][i] = number+1;

12                 number++;

13             }

14             up++;

15             

16             for(int i = up;i <= down;i++){

17                 matrix[i][right] = number+1;

18                 number++;

19             }

20             right--;

21             

22             for(int i = right;i >= left;i--){

23                 matrix[down][i] = number+1;

24                 number++;

25             }

26             down--;

27             

28             for(int i = down;i >= up;i--){

29                 matrix[i][left] = number+1;

30                 number++;

31             }

32             left++;

33         }

34         return matrix;

35     }

36 }