[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 ]
]

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

;
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));
}

}

第二遍记录：边界处理问题参考前一题。