permutations2.py

class Solution(object):
    def permuteUnique(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        nums = sorted(nums)
        temp = []
        result = []
        used = [0 for _ in range(len(nums))]
        self.backtracking(temp, result, nums, used)
        return result
        
    def backtracking(self, temp, result, nums, used):
        if(len(temp) == len(nums)):
            result.append(temp[:])    
        for i in range(0, len(nums)):
            if used[i] == 1: continue
            if i > 0 and nums[i] == nums[i - 1] and used[i - 1] == 0: continue
            used[i] = 1
            temp.append(nums[i])
            self.backtracking(temp, result, nums, used)
            temp.pop()
            used[i] = 0