这题挺有意思的，用状态机感觉会难，直接就 for 循环搞定。
class Solution(object):
def generateMatrix(self, n):
"""
:type n: int
:rtype: List[List[int]]
"""
result = [[0 for __ in range(n)] for _ in range(n)]
left, top, right, bottom = 0, 0, n-1, n-1
c = 1
while c <= n * n:
# 左到右
for i in range(left, right+1):
result[top][i] = c
c += 1
top += 1
# 右到下
for i in range(top, bottom+1):
result[i][right] = c
c += 1
right -= 1
# 右到左
for i in range(right, left-1, -1):
result[bottom][i] = c
c += 1
bottom -= 1
# 下到上
for i in range(bottom, top-1, -1):
result[i][left] = c
c += 1
left += 1
return result
