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;
        }
    }
?>

如果你不想重新发明轮子……http://lilurl.sourceforge.net/

您可以散列整个URL，但如果您只想缩短id，请按照marcel的建议进行。我写了这个Python实现:

https://gist.github.com/778542

Node.js和MongoDB的解决方案

因为我们知道MongoDB用来创建一个12字节的新ObjectId的格式。

一个4字节的值，表示从Unix纪元开始的秒数， 3字节的机器标识符， 2字节的进程id 一个3字节的计数器(在您的机器中)，从一个随机值开始。

示例(我选择一个随机序列) a1b2c3d4e5f6g7h8i9j1k2l3

a1b2c3d4表示自Unix纪元以来的秒数， 4e5f6g7表示机器标识符， H8i9表示进程号 J1k2l3表示计数器，从一个随机值开始。

由于计数器是唯一的，如果我们将数据存储在同一台机器上，我们可以毫无疑问地获得它，它将是重复的。

因此，短URL将是计数器，这里是一个代码片段，假设您的服务器运行正常。

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

// Create a schema
const shortUrl = new Schema({
    long_url: { type: String, required: true },
    short_url: { type: String, required: true, unique: true },
  });
const ShortUrl = mongoose.model('ShortUrl', shortUrl);

// The user can request to get a short URL by providing a long URL using a form

app.post('/shorten', function(req ,res){
    // Create a new shortUrl */
    // The submit form has an input with longURL as its name attribute.
    const longUrl = req.body["longURL"];
    const newUrl = ShortUrl({
        long_url : longUrl,
        short_url : "",
    });
    const shortUrl = newUrl._id.toString().slice(-6);
    newUrl.short_url = shortUrl;
    console.log(newUrl);
    newUrl.save(function(err){
        console.log("the new URL is added");
    })
});

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;
    }   
}

我将继续您的“将数字转换为字符串”方法。但是，如果您的ID是质数且大于52，您将意识到您提出的算法将失败。

理论背景

你需要一个双射函数f。这是必要的，这样你就可以为你的f(123) = 'abc'函数找到一个逆函数g('abc') = 123。这意味着:

一定不存在x1 x2 (x1≠x2)使得f(x1) = f(x2) 对于每一个y，你必须能找到一个x，使f(x) = y。

如何将ID转换为缩短的URL

Think of an alphabet we want to use. In your case, that's [a-zA-Z0-9]. It contains 62 letters. Take an auto-generated, unique numerical key (the auto-incremented id of a MySQL table for example). For this example, I will use 12510 (125 with a base of 10). Now you have to convert 12510 to X62 (base 62). 12510 = 2×621 + 1×620 = [2,1] This requires the use of integer division and modulo. A pseudo-code example: digits = [] while num > 0 remainder = modulo(num, 62) digits.push(remainder) num = divide(num, 62) digits = digits.reverse Now map the indices 2 and 1 to your alphabet. This is how your mapping (with an array for example) could look like: 0 → a 1 → b ... 25 → z ... 52 → 0 61 → 9 With 2 → c and 1 → b, you will receive cb62 as the shortened URL. http://shor.ty/cb

如何将缩短的URL解析为初始ID

反过来就更容易了。你只需要在字母表中反向查找。

E9a62将被解析为“字母表中的第4、61和0个字母”。 E9a62 = [4,61,0] = 4×622 + 61×621 + 0×620 = 1915810 现在找到WHERE id = 19158的数据库记录并执行重定向。

示例实现(由评论者提供)

c++ Python Ruby Haskell c# CoffeeScript Perl