using System;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        ShowAlternatives("+448700610100");

        ShowAlternatives("08700610100");

    }

​

    private static void ShowAlternatives(string number)

    {

        Console.WriteLine("Alternatives for {0}:", number);

        foreach (var alternative in GenerateAlternativeNumbers(number))

        {

            Console.WriteLine("    {0}", alternative);

        }

​

        Console.WriteLine();

    }

​

    private static string[] GenerateAlternativeNumbers(string matchAgainst)

    {

        matchAgainst = matchAgainst.Replace(" ", string.Empty);

        if (matchAgainst.StartsWith("+44"))

        {

            matchAgainst = matchAgainst.Replace("+44", "0");

        }

​

        return new string[]

        {

        matchAgainst.Insert(5, " "), matchAgainst.Insert(4, " "), matchAgainst.Insert(4, " ").Insert(8, " "), matchAgainst.ReplaceFirst("0", "+44"), matchAgainst.ReplaceFirst("0", "+44").Insert(6, " "), matchAgainst.ReplaceFirst("0", "+44").Insert(5, " ").Insert(9, " ")}

​

        ;

    }

}

​

static class StringReplace

{

    public static string ReplaceFirst(this string str, string initial, string replace)

    {

        if (!str.Contains(initial))

        {

            return str;

        }

​

        int index = str.IndexOf(initial);

        if (initial.Length != replace.Length)

        {

            bool initOrReplace = initial.Length < replace.Length;

            int diff = initOrReplace ? replace.Length - initial.Length : initial.Length - replace.Length;

            int count = 0;

            do

            {

                str = initOrReplace ? str.Insert(index, " ") : str.Remove(index, 1);

                count++;

            }

            while (count != diff);

        }

​

        char[] buffer = new char[str.Length];

        str.CopyTo(0, buffer, 0, str.Length);

        int j = 0;

        for (int i = index; i < index + replace.Length; i++)

        {

            buffer[i] = replace[j];

            j++;

        }

​

        StringBuilder sb = new StringBuilder();

        sb.Append(buffer);

        return sb.ToString();

    }

}