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 ]
]

与上一题相反，对矩阵赋值，步骤相同。
<pre name="code" class="java">public class Solution {
public int[][] generateMatrix(int n) {
int[][] result=new int

;
int rowstart = 0, rowend = n, colstart = 0, colend = n;
int num = 0;
while (num != n * n) {
// 上行
for (int i = colstart; i < colend; i++) {
result[rowstart][i]=num+1;
num++;
if (num == n * n)
return result;
}
rowstart++;
// 右列
for (int i = rowstart; i < rowend; i++) {
result[i][colend - 1]=num+1;
num++;
if (num == n * n)
return result;
}
colend--;
// 下行
for (int i = colend - 1; i >= colstart; i--) {
result[rowend - 1][i]=num+1;
num++;
if (num == n * n)
return result;
}
rowend--;
// 左列
for (int i = rowend - 1; i >= rowstart; i--) {
result[i][colstart]=num+1;
num++;
if (num == n * n)
return result;
}
colstart++;
}
return result;
}
}