Encode and Decode TinyURL
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.
想了下可能的重复编码问题,直接用HashMap做了短URL和长URL的映射.将数字和字母混合编码,按题目的6位数的编码的话可以达到\(36^6\)种编码,理论上性能是ok的.
代码如下
public class Codec { ???HashMap<String, String> enIndex = new HashMap<String, String>(); ???HashMap<String,String>deIndex = new HashMap<String, String>(); ???String keyset = "0123456789abcdefghijklmnopqrstuvwyz"; ???String tinyUrlBase = "http://tinyurl.com/"; ???// Encodes a URL to a shortened URL. ???public String encode(String longUrl) { ???????String key; ???????if (enIndex.containsKey(longUrl)) return enIndex.get(longUrl); ???????do{ ???????????StringBuilder sb = new StringBuilder(); ???????????for(int i =0 ; i<6;i++){ ???????????????sb.append(keyset.charAt((int) (Math.random()*keyset.length()))); ???????????} ???????????key = sb.toString(); ???????}while(deIndex.containsKey(key)); ???????deIndex.put(key,longUrl); ???????enIndex.put(longUrl, tinyUrlBase+key); ???????return tinyUrlBase+key; ???} ???// Decodes a shortened URL to its original URL. ???public String decode(String shortUrl) { ???????return deIndex.get(shortUrl.replace(tinyUrlBase,"")); ???}}写完看了下排名.....貌似蛮低的.不过这题感觉是比较自由,应该不会太卡时间的,感觉就是考虑怎么编码好点.
前面的方案大致有:
- 用计数器编码
那么当前服务器存了多少url就曝露出来了，也许会有安全隐患。而且计数器编码另一个缺点就是数字会不断的增大 - 直接返回参数(最快)
....这道题的OJ基本上是形同虚设，两个函数分别直接返回参数字符串也能通过OJ，囧
Encode and Decode TinyURL
原文地址：http://www.cnblogs.com/Dyleaf/p/7965782.html