Euler17.cs

/*
If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 
letters used in total.

If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 
(one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage.
*/

using System;

class Program
{
    static string GetNumberName(int input)
    {
        var output = new System.Text.StringBuilder();

        string[] fromOneToNineteen = {"", "one", "two", "three", "four", "five",
                                    "six", "seven", "eight", "nine", "ten", "eleven",
                                    "twelve", "thirteen", "fourteen", "fifteen", "sixteen",
                                    "seventeen", "eighteen", "nineteen" };

        string[] decimalsNames = {"", "", "twenty", "thirty", "forty", "fifty",
                                "sixty", "seventy", "eighty", "ninety"};

        string[] hundredsNames = {"", "onehundred", "twohundred", "threehundred", "fourhundred",
                               "fivehundred", "sixhundred", "sevenhundred", "eighthundred", "ninehundred"};



        int hundreds = input / 100; 
        int decimals = (input / 10) - hundreds * 10; 
        int units = input % 10; 

        if (input >= 100 && input <= 999)
        {
            if (decimals < 2)
            {
                if (units == 0 && decimals == 0)
                {
                    output.Append(hundredsNames[hundreds]);
                }
                else
                {
                    output.AppendFormat("{0}and{1}", hundredsNames[hundreds], fromOneToNineteen[input % 100]);
                }
            }
            else
            {
                output.AppendFormat("{0}and{1}{2}", hundredsNames[hundreds],
                    decimalsNames[decimals], fromOneToNineteen[units]);
            }
        }
        else if (input >= 20 && input <= 99)
        {
            output.AppendFormat("{0}{1}", decimalsNames[decimals], fromOneToNineteen[units]);
        }
        else if (input >= 0 && input < 20)
        {
            if (input == 0)
            {
                output.AppendFormat("zero");
            }
            output.AppendFormat("{0}", fromOneToNineteen[input]);
        }
        else if (input == 1000)
        {
            return "onethousand";
        }

        return output.ToString();
    }
    static void Main()
    {
        int lettersCount = 0;

        for (int i = 1; i <= 1000; i++)
        {
            lettersCount += GetNumberName(i).Length;
        }
        
        Console.WriteLine(lettersCount);
    }
}