leetcode -- Spiral Matrix I&II -- 简单，但需要优化

class Solution(object):
def generateMatrix(self, n):
"""
:type n: int
:rtype: List[List[int]]
"""
if n == 0: return []
m, n = n, n
matrix = [[0]*n for x in range(n)]

i,j = 0, 0
count = 0
val = 1
while i < m and j < n and matrix[i][j] == 0:
start_i, start_j = i, j
end_i, end_j = m - count - 1, n - count - 1

if i == end_i:
for k in xrange(start_j, end_j + 1):
matrix[i][k] = val
val += 1
break
if j == end_j:
for k in xrange(start_i, end_i + 1):
matrix[i][k] = val
val += 1
break

while j<=end_j:
matrix[i][j] = val
val += 1
j += 1
j -= 1
i += 1
while i<=end_i:
matrix[i][j] = val
val += 1
i += 1
i -= 1
j -= 1
while j>=start_j:
matrix[i][j] = val
val += 1
j -= 1
j += 1
i -= 1
while  i>start_i:#exclude the mat[i][j]

matrix[i][j] = val
val += 1
i -= 1

i, j = i + 1, j + 1
count += 1
return matrix