1import java.util.ArrayList;
2import java.util.Arrays;
3import java.util.List;
4
5public class PermutationsUnique {
6    public List<List<Integer>> permuteUnique(int[] nums) {
7        List<List<Integer>> results = new ArrayList<>();
8        Arrays.sort(nums);
9        backtrack(nums, new boolean[nums.length], new ArrayList<>(), results);
10        return results;
11    }
12
13    private void backtrack(int[] nums, boolean[] used, List<Integer> current, List<List<Integer>> results) {
14        if (current.size() == nums.length) {
15            results.add(new ArrayList<>(current));
16            return;
17        }
18        for (int i = 0; i < nums.length; i++) {
19            if (used[i] || (i > 0 && nums[i] == nums[i - 1] && !used[i - 1])) {
20                continue;
21            }
22            used[i] = true;
23            current.add(nums[i]);
24            backtrack(nums, used, current, results);
25            used[i] = false;
26            current.remove(current.size() - 1);
27        }
28    }
29
30    public static void main(String[] args) {
31        PermutationsUnique pu = new PermutationsUnique();
32        System.out.println(pu.permuteUnique(new int[]{1, 1, 2}));
33    }
34}

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));
        }
    }
}