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 ]]

https://oj.leetcode.com/problems/spiral-matrix-ii/

思路：按要求输出，注意边界。

public class Solution {	public int[][] generateMatrix(int n) {		int[][] mat = new int[n][n];		if (n <= 0)			return mat;		int num = 1;		int left = 0;		int right = n - 1;		int top = 0;		int bottom = n - 1;		while (num <= n * n) {			int i;			for (i = left; i <= right; i++)				mat[top][i] = num++;			for (i = top + 1; i <= bottom; i++)				mat[i][right] = num++;			if (top < bottom)				for (i = right - 1; i >= left; i--)					mat[bottom][i] = num++;			if (left < right)				for (i = bottom - 1; i >= top + 1; i--)					mat[i][left] = num++;			top++;			left++;			bottom--;			right--;		}		return mat;	}	public static void main(String[] args) {		System.out.println(new Solution().generateMatrix(1));	}}