Encode and Decode TinyURL
2017-12-03 12:14
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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
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