Question

Trying to build upon the answers in this thread [ Alphanumeric Counter ] to build an endless (for any int) alphanumeric counter without padding.

I want to create a counter that starts at 0 and counts something like this.

0,1,2…Y,Z,10,11,12…1Y,1Z,20,21…ZY,ZZ,100,101…ZZZ,1000,1001 .. infinity (overflow)….

The purpose of the counter is to create short URLS from my database INT id’s. I want to input the id of the row and get a base 36 value from it that i can use as the url.

I’ve made a few attempts but they all seem to end up wrong. I’m getting stuck on how I can test when I should increase the number of characters. i.e. go from Z to 10 or from ZZ to 100.

Answer 1

I think this is what you want:

using System;
using System.Collections.Generic;

class Test
{
    static void Main()
    {
        foreach (string x in EndlessBase64Sequence())
        {
            Console.WriteLine(x);
        }
    }

    private static char NextBase36Char(char c)
    {
        if ((c >= '0' && c <= '8') ||
            (c >= 'A' && c <= 'Z'))
        {
            return (char) (c + 1);
        }
        if (c == '9')
        {
            return 'A';
        }
        throw new ArgumentException();
    }

    public static IEnumerable<string> EndlessBase64Sequence()
    {
        char[] chars = { '0' };

        while (true)
        {
            yield return new string(chars);

            // Move to the next one...
            bool done = false;
            for (int position = chars.Length - 1; position >= 0; position--)
            {
                if (chars[position] == 'Z')
                {
                    chars[position] = '0';
                }
                else
                {
                    done = true;
                    chars[position] = NextBase36Char(chars[position]);
                    break;
                }
            }
            // Need to expand?
            if (!done)
            {
                chars = new char[chars.Length + 1];
                chars[0] = '1';
                for (int i = 1; i < chars.Length; i++)
                {
                    chars[i] = '0';
                }
            }
        }
    }
}