Array Matcher

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ArrayMatcher
{
    class ArrayMatcher
    {
        static void Main(string[] args)
        {
            string inputDate = Console.ReadLine();
            string[] date = inputDate.Split('\\');
            char[] leftArray = date[0].ToCharArray();
            char[] rightArray = date[1].ToArray();
            List<char> output = new List<char>();
            int flag = 0;
            if (date[2] == "join")
            {
                for (int i = 0; i < rightArray.Length; i++)
                {
                    for (int j = 0; j < leftArray.Length; j++)
                    {
                        if (leftArray[j] == rightArray[i])
                        {
                            output.Add(leftArray[j]);
                        }
                    }
                }


            }
            else if (date[2] == "left exclude")
            {
                for (int i = 0; i < rightArray.Length; i++)
                {
                    for (int j = 0; j < leftArray.Length; j++)
                    {
                        if (rightArray[i] == leftArray[j])
                        {
                            flag++;
                        }

                    }
                        if(flag==0)output.Add(rightArray[i]);
                        flag = 0;
                }
            }
            else if (date[2] == "right exclude")
            {
                for (int i = 0; i < leftArray.Length; i++)
                {
                    for (int j = 0; j < rightArray.Length; j++)
                    {
                        if (leftArray[i] == rightArray[j])
                        {
                            flag++;
                        }

                    }
                    if (flag == 0) output.Add(leftArray[i]);
                    flag = 0;
                }
            }
            output.Sort();
            string outputString = string.Join("", output);
            Console.WriteLine(outputString);

        }
    }
}