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Short code generator.Converts a long integer to a "short code" (a seemingly random string of characters - as seen on many popular URL Shortener utilities.) and vice-versa.See: http://stackoverflow.com/a/529852/57477
using System;
namespace ShortCodes
{
public static class ShortCodes
{
// You may change the "shortcode_Keyspace" variable to contain as many or as few characters as you
// please. The more characters that are included in the "shortcode_Keyspace" constant, the shorter
// the codes you can produce for a given long.
private static string shortcodeKeyspace = "abcdefghijklmnopqrstuvwxyz0123456789";
// NOTE: This "SetKeyspace" method is only added to the class to allow the unit tests to
// arbitrarily set new keyspace "constants" to facilitate testing with different
// keyspace values. You can safely remove this "SetKeyspace" method and hard-code
// your own shortcodeKeyspace for real-world use.
public static void SetKeyspace(string keyspace)
{
shortcodeKeyspace = keyspace;
}
public static string LongToShortCode(long number)
{
// Guard clause. If passed 0 as input
// we always return empty string.
if (number == 0)
{
return string.Empty;
}
var keyspaceLength = shortcodeKeyspace.Length;
var shortcodeResult = "";
var numberToEncode = number;
var i = 0;
do
{
i++;
var characterValue = numberToEncode % keyspaceLength == 0 ? keyspaceLength : numberToEncode % keyspaceLength;
var indexer = (int) characterValue - 1;
shortcodeResult = shortcodeKeyspace[indexer] + shortcodeResult;
numberToEncode = ((numberToEncode - characterValue) / keyspaceLength);
}
while (numberToEncode != 0);
return shortcodeResult;
}
public static long ShortCodeToLong(string shortcode)
{
var keyspaceLength = shortcodeKeyspace.Length;
long shortcodeResult = 0;
var shortcodeLength = shortcode.Length;
var codeToDecode = shortcode;
foreach (var character in codeToDecode)
{
shortcodeLength--;
var codeChar = character;
var codeCharIndex = shortcodeKeyspace.IndexOf(codeChar);
if (codeCharIndex < 0)
{
// The character is not part of the keyspace and so entire shortcode is invalid.
return 0;
}
try
{
checked
{
shortcodeResult += (codeCharIndex + 1) * (long) (Math.Pow(keyspaceLength, shortcodeLength));
}
}
catch(OverflowException)
{
// We've overflowed the maximum size for a long (possibly the shortcode is invalid or too long).
return 0;
}
}
return shortcodeResult;
}
}
}
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