给定一个可包含重复数字的序列，返回所有不重复的全排列。
示例:
输入: [1,1,2]
输出:
[
[1,1,2],
[1,2,1],
[2,1,1]
]
import copy
class Solution:
def permuteUnique(self, nums):
"""
:type nums: List[int]
:rtype: List[List[int]]
"""
res = []
nums.sort()
self.back_track(res, nums, 0)
return res
def back_track(self, res, nums, n):
nums = copy.deepcopy(nums)
if n == len(nums)-1:
temp = copy.deepcopy(nums)
res.append(temp)
else:
for i in range(n, len(nums)):
if i != n and nums[i] == nums[n]:
continue
nums[n], nums[i] = nums[i], nums[n]
self.back_track(res, nums, n+1)
