Задание 13

//Удалить из сообщения все повторяющиеся слова.
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace mainSolution
{

    static class Program
    {
        static void Trim(ref string s)
        {
            s = s.Trim();
            StringBuilder res = new StringBuilder();
            res.Append(s[0]);
            for (int i = 1; i < s.Length; ++i)
                if (s[i] != char.ToLower(s[i - 1]))
                    res.Append(s[i]);
            s = res.ToString();
        }
        static void Main(string[] args)
        {
            using (StreamReader inp = new StreamReader("D:/input.txt"))
            {

                Regex Delete_Arcticles = new Regex(@"\b(([Tt]he)|([Aa]n)|([Aa]))\b");


                Regex Ce_To_Se = new Regex("Ce");
                Regex Ci_To_Si = new Regex("Ci");

                Regex ce_To_se = new Regex("ce");
                Regex ci_To_si = new Regex("ci");

                Regex ck_To_k = new Regex(@"ck|c");
                Regex Ck_To_K = new Regex(@"ck|C");

                Regex ee_TO_i = new Regex("ee");
                Regex Ee_TO_I = new Regex("Ee");

                Regex Two_any_To_One = new Regex(@"([a-z | A-Z])\1+");

                Regex Delete_solo_e = new Regex(@"\s[E,e]\s");

                Regex Delete_space = new Regex(@"(\s)\1+|\s$");


                string s = inp.ReadToEnd();

                string ans = s;
                ans = Regex.Replace(ans, Delete_Arcticles.ToString(), "");
                ans = Regex.Replace(ans, Ci_To_Si.ToString(), "Si");
                ans = Regex.Replace(ans, ci_To_si.ToString(), "si");

                ans = Regex.Replace(ans, Ce_To_Se.ToString(), "Se");
                ans = Regex.Replace(ans, ce_To_se.ToString(), "se");

                ans = Regex.Replace(ans, ck_To_k.ToString(), "k");
                ans = Regex.Replace(ans, Ck_To_K.ToString(), "K");

                ans = Regex.Replace(ans, ee_TO_i.ToString(), "i");
                ans = Regex.Replace(ans, Ee_TO_I.ToString(), "I");

                ans = Regex.Replace(ans, Two_any_To_One.ToString(), "$1");

                ans = Regex.Replace(ans, Delete_solo_e.ToString(), "");

                ans = Regex.Replace(ans, Delete_space.ToString(), "$1");

                Trim(ref ans);

                Console.WriteLine(ans);
            }
        }

    }
}