using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

public class Program {

    private static readonly Regex WordsRegex = new Regex(@"[\p{L}']+"); 

​

    private static List<(string word, int presentAt)> MyWords(string text1, string text2) {

      HashSet<string> words1 = WordsRegex

        .Matches(text1)

        .Cast<Match>()

        .Select(match => match.Value)

        .ToHashSet(StringComparer.OrdinalIgnoreCase);

​

      HashSet<string> words2 = WordsRegex

        .Matches(text2)

        .Cast<Match>()

        .Select(match => match.Value)

        .ToHashSet(StringComparer.OrdinalIgnoreCase);

​

      return words1

        .Union(words2)

        .Select(word => (word, presentAt: (words1.Contains(word) ? 1 : 0) | (words2.Contains(word) ? 2 : 0)))

        .ToList();

    }

    public static void Main()

    {

        string str1 = "Cat meet's a dog has";

        string str2 = "Cat meet's a dog and a bird";

        var result = MyWords(str1, str2);

        var report = string.Join(Environment.NewLine, result);

        Console.WriteLine(report);

        Console.WriteLine();

        string[] options = new string[] {

            "not present",

            "present in first string not present in second string",

            "not present in first string but present in second string",

            "present in first string and present in second string",

        };

        var report2 = string.Join(Environment.NewLine, result

            .Select(pair => $"{pair.word} - {options[pair.presentAt]}"));

        Console.Write(report2);

    }

}