1def permuteUnique(nums):
2    def backtrack(combination, used):
3        if len(combination) == len(nums):
4            results.append(list(combination))
5            return
6
7        for i in range(len(nums)):
8            if used[i] or i > 0 and nums[i] == nums[i-1] and not used[i-1]:
9                continue
10            used[i] = True
11            combination.append(nums[i])
12            backtrack(combination, used)
13            used[i] = False
14            combination.pop()
15
16    results = []
17    nums.sort()
18    backtrack([], [False] * len(nums))
19    return results
20
21print(permuteUnique([1, 1, 2]))

1using System;
2using System.Collections.Generic;
3
4class PermutationsUniqueSwapSet {
    public IList<IList<int>> PermuteUnique(int[] nums) {
        var results = new HashSet<string>();
        Permute(nums, 0, results);
        var listResults = new List<IList<int>>();
        foreach(var res in results) {
            var lst = new List<int>();
            foreach(var c in res.Split(',')) {
                lst.Add(int.Parse(c));
            }
            listResults.Add(lst);
        }
        return listResults;
    }

    private void Permute(int[] nums, int start, HashSet<string> results) {
        if (start == nums.Length) {
            results.Add(string.Join(",", nums));
            return;
        }
        for (int i = start; i < nums.Length; i++) {
            Swap(nums, start, i);
            Permute(nums, start + 1, results);
            Swap(nums, start, i);
        }
    }

    private void Swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }

    static void Main() {
        var solution = new PermutationsUniqueSwapSet();
        var result = solution.PermuteUnique(new[] { 1, 1, 2 });
        foreach (var perm in result) {
            Console.WriteLine(string.Join(",", perm));
        }
    }
}