public class UrlShortener {
    private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    private static final int    BASE     = ALPHABET.length();

    public static String encode(int num) {
        StringBuilder sb = new StringBuilder();
        while ( num > 0 ) {
            sb.append( ALPHABET.charAt( num % BASE ) );
            num /= BASE;
        }
        return sb.reverse().toString();   
    }

    public static int decode(String str) {
        int num = 0;
        for ( int i = 0; i < str.length(); i++ )
            num = num * BASE + ALPHABET.indexOf(str.charAt(i));
        return num;
    }   
}

你是故意省略O 0和i的吗?

我刚刚基于Ryan的解决方案创建了一个PHP类。

<?php

    $shorty = new App_Shorty();

    echo 'ID: ' . 1000;
    echo '<br/> Short link: ' . $shorty->encode(1000);
    echo '<br/> Decoded Short Link: ' . $shorty->decode($shorty->encode(1000));


    /**
     * A nice shorting class based on Ryan Charmley's suggestion see the link on Stack Overflow below.
     * @author Svetoslav Marinov (Slavi) | http://WebWeb.ca
     * @see http://stackoverflow.com/questions/742013/how-to-code-a-url-shortener/10386945#10386945
     */
    class App_Shorty {
        /**
         * Explicitly omitted: i, o, 1, 0 because they are confusing. Also use only lowercase ... as
         * dictating this over the phone might be tough.
         * @var string
         */
        private $dictionary = "abcdfghjklmnpqrstvwxyz23456789";
        private $dictionary_array = array();

        public function __construct() {
            $this->dictionary_array = str_split($this->dictionary);
        }

        /**
         * Gets ID and converts it into a string.
         * @param int $id
         */
        public function encode($id) {
            $str_id = '';
            $base = count($this->dictionary_array);

            while ($id > 0) {
                $rem = $id % $base;
                $id = ($id - $rem) / $base;
                $str_id .= $this->dictionary_array[$rem];
            }

            return $str_id;
        }

        /**
         * Converts /abc into an integer ID
         * @param string
         * @return int $id
         */
        public function decode($str_id) {
            $id = 0;
            $id_ar = str_split($str_id);
            $base = count($this->dictionary_array);

            for ($i = count($id_ar); $i > 0; $i--) {
                $id += array_search($id_ar[$i - 1], $this->dictionary_array) * pow($base, $i - 1);
            }
            return $id;
        }
    }
?>

对于一个类似的项目，为了获得一个新键，我围绕一个随机字符串生成器创建了一个包装器函数，该函数调用生成器，直到我得到一个尚未在哈希表中使用过的字符串。一旦名称空间开始满了，这个方法就会变慢，但正如您所说的，即使只有6个字符，也有足够的名称空间可以使用。

要获得高质量的Node.js / JavaScript解决方案，请参阅id缩短器模块，该模块经过了全面测试，已经在生产环境中使用了几个月。

它提供了一个有效的id / URL缩短支持的可插拔存储默认为Redis，你甚至可以自定义你的短id字符集，是否缩短是幂等的。这是一个重要的区别，并不是所有的URL缩短器都考虑在内。

相对于这里的其他答案，这个模块实现了上面Marcel Jackwerth的优秀的公认答案。

解决方案的核心由下面的Redis Lua代码段提供:

local sequence = redis.call('incr', KEYS[1])

local chars = '0123456789ABCDEFGHJKLMNPQRSTUVWXYZ_abcdefghijkmnopqrstuvwxyz'
local remaining = sequence
local slug = ''

while (remaining > 0) do
  local d = (remaining % 60)
  local character = string.sub(chars, d + 1, d + 1)

  slug = character .. slug
  remaining = (remaining - d) / 60
end

redis.call('hset', KEYS[2], slug, ARGV[1])

return slug

这是我的PHP 5类。

<?php
class Bijective
{
    public $dictionary = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    public function __construct()
    {
        $this->dictionary = str_split($this->dictionary);
    }

    public function encode($i)
    {
        if ($i == 0)
        return $this->dictionary[0];

        $result = '';
        $base = count($this->dictionary);

        while ($i > 0)
        {
            $result[] = $this->dictionary[($i % $base)];
            $i = floor($i / $base);
        }

        $result = array_reverse($result);

        return join("", $result);
    }

    public function decode($input)
    {
        $i = 0;
        $base = count($this->dictionary);

        $input = str_split($input);

        foreach($input as $char)
        {
            $pos = array_search($char, $this->dictionary);

            $i = $i * $base + $pos;
        }

        return $i;
    }
}

为什么要使用哈希呢?

您只需将自动递增值简单地转换为字母数字值。你可以通过使用一些基数转换很容易做到这一点。假设您的字符空间(a-z, a-z, 0-9等)有62个字符，将id转换为以40为基数的数字并使用这些字符作为数字。