using System;

using System.Collections.Generic;

public class Program

{   

    public static int SingleNumber(int[] nums) {

        int result = 0;

        foreach(int num in nums){

            result ^= num;

        }

        return result;

    }

    public static int SingleNumberHashed(int[] nums) {

        Dictionary<int, bool> dataTable = new Dictionary<int, bool>();

        foreach(int num in nums){

            if(dataTable.ContainsKey(num))

                dataTable[num] = false;

            else

                dataTable.Add(num, true);

        }

        for(int i = 0; i < nums.Length; i++){

            if(dataTable[nums[i]])

                return nums[i];

        }

        return -1;

    }

    public static int[] SingleNumber3(int[] nums) {

        Dictionary<int, bool> dataTable = new Dictionary<int, bool>();

        List<int> result = new List<int>();

        foreach(int num in nums){

            if(dataTable.ContainsKey(num))

                dataTable[num] = false;

            else

                dataTable.Add(num, true);

        }

        for(int i = 0; i < nums.Length; i++){

            if(dataTable[nums[i]])

                result.Add(nums[i]);

        }

        return result.ToArray();

    }

    public static void Main()

    {

        Console.WriteLine(SingleNumberHashed(new int [] {1,2,1,2,4}));

        Console.WriteLine(SingleNumber(new int [] {2,2,3,2}));

        var SingleNumber3Collection = SingleNumber3(new int [] {0,1,0,1,0,1,99});

        foreach(var item in SingleNumber3Collection){

            Console.Write(item);        

        }

    }

}