С# Essential_1

public class Mixing
{
    public static string Mix(string s1, string s2)
    {
        int countForFirstString;
        int countForSecondString;
        List<string> unorderedMixedStrings = new();
        string mixedSortedString = "";

        var listOfOnlyLetters = from char s in s1.Union(s2)
                            where char.IsLower(s)
                            where char.IsLetter(s)
                            select s;

        foreach (char l in listOfOnlyLetters)
        {
            string adding = "";
            countForFirstString = s1.Count(s => s == l);
            countForSecondString = s2.Count(s => s == l);

            if (countForFirstString > 1 || countForSecondString > 1)
            {
                if (countForFirstString > countForSecondString)
                    adding = $"1:{String.Concat(Enumerable.Repeat(l, countForFirstString))}/";

                if (countForFirstString < countForSecondString)
                    adding = $"2:{String.Concat(Enumerable.Repeat(l, countForSecondString))}/";

                if (countForFirstString == countForSecondString)
                    adding = $"3:{String.Concat(Enumerable.Repeat(l, countForFirstString))}/";

                unorderedMixedStrings.Add(adding);
            }
        }
        if (unorderedMixedStrings.Count == 0) { return ""; };
        var OrderedMexedStrings = from s in unorderedMixedStrings
                         orderby s.Length descending,
                         s ascending,
                         s[2] ascending
                         select s;

        
        var replacedNames = OrderedMexedStrings.Select(x => x.Replace('3', '='));

        foreach (string strr in replacedNames)
        {
            foreach (char ch in strr)
                mixedSortedString += ch;
        }
        return mixedSortedString[..^1];
        
    }
}