[leetcode] 535：短域名编码和解码

TinyURL设计与实现

最新推荐文章于 2022-06-29 14:30:18 发布

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本文介绍了一种短域名服务的设计方案，使用HashMap保存长域名与短域名间的映射关系，确保每个长域名都能被编码为唯一的短域名，并能正确解码回原始长域名。

Description：

TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk.

Design the encode and decode methods for the TinyURL service. There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL.

设计一个短域名的编码和解码和解码方法，例如长域名https://leetcode.com/problems/design-tinyurl 对应的短域名是 http://tinyurl.com/4e9iAk

Solution

用HashMap来保存长域名和短域名之间的映射关系

public class TinyUrl {
    private static final String TINY_URL_BASE = "http://tinyurlbase.com/";
    private static final String DIC = "0123456789qwertyuiopasdfghjklzxcvbnm";
    private static final int DIC_LENGTH = DIC.length();
    /**
     * hash字符串的长度
     */
    private static final int HASH_LENGTH = 7;

    /**
     * 保存hash字符串和url之间的映射关系
     */
    private Map<String, String> hashToUrl;
    private Map<String, String> urlToHash;
    Random random;

    public TinyUrl() {
        hashToUrl = new HashMap<>();
        urlToHash = new HashMap<>();
        random = new Random();
    }

    public String encode(String longUrl){
        if (urlToHash.containsKey(longUrl)){
            return TINY_URL_BASE + urlToHash.get(longUrl);
        }

        //随机生成hash值
        StringBuilder hashBuilder = new StringBuilder();
        do{
            for (int i = 0; i < HASH_LENGTH; i++){
                random.setSeed(System.nanoTime());
                hashBuilder.append(DIC.charAt(random.nextInt(DIC_LENGTH)));
            }
        }while (hashToUrl.containsKey(hashBuilder.toString()));

        hashToUrl.put(hashBuilder.toString(), longUrl);
        urlToHash.put(longUrl, hashBuilder.toString());

        return TINY_URL_BASE + hashBuilder.toString();
    }

    public String decode(String shortUrl){
        int lastBackslashPos = shortUrl.lastIndexOf('/') + 1;
        return hashToUrl.get(shortUrl.substring(lastBackslashPos));
    }

    public static void main(String[] args) {
        TinyUrl tinyUrl = new TinyUrl();
        String shortUrl = tinyUrl.encode("https://leetcode.com/problems/design-tinyurl");
        String longUrl = tinyUrl.decode(shortUrl);
        System.out.println(shortUrl);
        System.out.println(longUrl);
    }
}