Given an array of positive integers, print out all the numbers which are repeated an even number of times without using additional storage

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text.RegularExpressions;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            //This part assumes that all the elements in the array lie in the range (min,min + arraylength -1).
            int[] arr1 = { 1, 2, 3, 4, 4, 5, 2, 1, 1, 1 };
            int count = 1;
            int min = arr1.Min();
            int max = arr1.Max();
            for (int i = 0; i < arr1.GetLength(0); i++)
            {
                arr1[Math.Abs(arr1[i])] *= -1;
            }
            for (int i = 0; i < arr1.GetLength(0); i++)
            {
                Console.Write(arr1[i] + " ");
            }
            Console.WriteLine();
            for (int i = min; i <= max; i++)             {                 if (arr1[i] > 0)
                {
                    Console.Write(i + " ");
                }
            }
            Console.WriteLine();
            //This part sorts the array and finds the frequency map and counts the frequency of each element.
            int[] arr2 = { 1, 2, 3, 4, 4, 5, 2, 1, 1, 1 };
            Array.Sort(arr2);
            for (int i = 0; i < arr2.GetLength(0) - 1; i++)
            {
                count = 1;
                while (arr2[i + 1] == arr2[i])
                {
                    i++;
                    count++;
                }
                if (count % 2 == 0)
                {
                    Console.WriteLine(arr2[i] + " " + count);
                }
            }
        }
    }
}