LeetCode #535 - Encode and Decode TinyURL-优快云博客

本文介绍了一种URL缩短服务的设计方案，使用TinyURL将长URL转换为短链接，并确保其可逆性。通过随机生成固定长度的token表示编码后的URL，结合哈希表存储编码和解码对应关系，实现了URL的高效编码与解码。

题目描述：

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.

随机生成固定长度的token表示编码后的URL，同时用哈希表存储URL编码和解码对应的结果。

class Solution {
public:
    // Encodes a URL to a shortened URL.
    string encode(string longUrl) {
        if(long_to_short.count(longUrl)) return long_to_short[longUrl];
        else
        {
            string s;
            for(int i=0;i<8;i++) s.push_back(chars[rand()%chars.size()]);
            if(long_to_short.count(s)>0) return encode(longUrl);
            else
            {
                long_to_short[longUrl]=s;
                short_to_long[s]=longUrl;
            }
            return s;
        }
    }

    // Decodes a shortened URL to its original URL.
    string decode(string shortUrl) {
        return short_to_long[shortUrl];
    }
    
private:
    unordered_map<string,string> short_to_long;
    unordered_map<string,string> long_to_short;
    string chars="0123456789abcdefghijklmnopqrstuvwxyz";
};