using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var time = "1 800 RED CrOSS";

        Console.WriteLine(TranslateVanityNumbers(time));

        Console.WriteLine("1-800-733-276");

    }

​

    public static string TranslateVanityNumbers(string phoneNumber)

    {

        IEnumerable<char> takeNthDigits(IEnumerable<char> source, int limit)

        {

            var count = 0;

            return source.Select(it => (it, count += char.IsLetterOrDigit(it) ? 1 : 0)).TakeWhile(p => p.Item2 <= limit).Select(x => x.it);

        }

​

        // we should use a dictionary here but switch expression are funnier

        return string.Concat(takeNthDigits(phoneNumber, 10).Select(c => char.ToUpper(c) switch

        {

            'A' or 'B' or 'C' => '2',

            'E' or 'D' or 'F' => '3',

            'G' or 'H' or 'I' => '4',

            'J' or 'K' or 'L' => '5',

            'M' or 'N' or 'O' => '6',

            >= 'P'and <= 'S'  => '7',

            'T' or 'U' or 'V' => '8',

            'X' or 'Y' or 'Z' => '9',

            _ => c

        }));

    }

}