Function code for generating the short URL from an integer key

function.cs

public static readonly string Alphabet = "abcdefghijklmnopqrstuvwxyz0123456789";
public static readonly int Base = Alphabet.Length;

public static string Encode(int i)
{
  if (i == 0)
  {
    return Alphabet[0].ToString();
  }
  var s = string.Empty;
  while (i > 0)
  {
      s += Alphabet[i % Base];
      i = i / Base;
  }

  return string.Join(string.Empty, s.Reverse());
}