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：
这道题跟Spiral Matrix想法也是类似的，就是依照矩阵从外圈到内圈建立。
要考虑如果是奇数行列的话，最中心的那个点要单加。 代码如下：
1 public int[][] generateMatrix(int n) {
2 int[][] res = new int[n][n];
3 int k = 1;
4 int top = 0, bottom = n - 1, left = 0, right = n - 1;
5 while (left < right && top < bottom) {
6 for (int j = left; j < right; j++) {
7 res[top][j] = k++;
8 }
9 for (int i = top; i < bottom; i++) {
res[i][right] = k++;
}
for (int j = right; j > left; j--) {
res[bottom][j] = k++;
}
for (int i = bottom; i > top; i--) {
res[i][left] = k++;
}
left++;
right--;
top++;
bottom--;
}
if (n % 2 != 0)
res[n / 2][n / 2] = k;
return res;
}
Reference：leetcodenotes.wordpress.com/2013/11/23/leetcode-spiral-matrix-%E6%8A%8A%E4%B8%80%E4%B8%AA2d-matrix%E7%94%A8%E8%9E%BA%E6%97%8B%E6%96%B9%E5%BC%8F%E6%89%93%E5%8D%B0/