LeetCode51题N皇后为何本地调正确，上传输出为空？
代码如下：
class Solution(object):
def solveNQueens(self, n):
"""
:type n: int
:rtype: List[List[str]]
"""
def judge (x,y,own): #判断同行、列、对角线是否有皇后
for i in range(len(own)):
if x == own[i][0] or y == own[i][1] or abs((x-own[i][0])/(y-own[i][1])) == 1:
return False
return True
def back(x,own): #回溯，x为行，j为列，own为已经有皇后的格子坐标
if x == n:
temp = []
for i in range(len(own)):
temp.append('.'*own[i][1]+'Q'+'.'*(n-1-own[i][1]))
ans.append(temp)
return
for j in range(n):
if judge(x,j,own):
own.append([x,j])
back(x+1,own)
own.pop()
ans = []
back(0,[])
return ans 本地测试能够输出答案，但是上传LeetCode输出[]，想了一下午都没想明白。。。求教！！！
