using System;

using System.Text;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int[] nums = {-1,0,1,-1,2,-4};

        IList<IList<int>> list = ThreeSum(nums);

        foreach (var l in list)

            PrintList(l);

    }

    public static IList<IList<int>> ThreeSum(int[] nums) {

        IList<IList<int>> sets = new List<IList<int>>();

        Hashtable solutions = new Hashtable();

        if (nums.Length < 3)

            return sets;

        Array.Sort(nums);

        if (nums[0] == 0 && nums[0] == nums[nums.Length - 1]) {

            sets.Add(new List<int> {nums[0], nums[0], nums[0]});

            return sets;

        }

        int i = 0;

        while (i < nums.Length - 2)

        {

            int target = 0 - nums[i];

            Dictionary<int, int> dict = new Dictionary<int, int>();

            int val;

​

            for (int j = i + 1; j < nums.Length; j++)

            {

                if (dict.TryGetValue(nums[j], out val)) {

                    List<int> list = new List<int> {nums[i], val, nums[j]};

                    string key = string.Concat(list);

                    if (!solutions.ContainsKey(key)) {

                        sets.Add(list);

                        solutions.Add(key, null);

                    }

                }

                else if (!dict.TryGetValue(target-nums[j], out val))

                    dict.Add(target-nums[j], nums[j]);

            }

            int curr = nums[i];

            while (i < nums.Length && nums[i] == curr)

                i++;

        }

        return sets;

    }

    public static void PrintList(IList<int> list)

    {

        StringBuilder sb = new StringBuilder();

        foreach (var i in list)

            sb.Append(i + ", ");

        sb.Length -= 2;

        Console.Write("[{0}]\n", sb);

    }

}