Encode and Decode TinyURL — HashMap Bidirectional Mapping

# Python
import random, string

class Codec:
    def __init__(self):
        self.enc = {}  # short -> long
        self.dec = {}  # long -> short
        self.base = "http://tinyurl.com/"

    def encode(self, longUrl: str) -> str:
        if longUrl not in self.dec:
            key = ''.join(random.choices(string.ascii_letters + string.digits, k=6))
            while key in self.enc:
                key = ''.join(random.choices(string.ascii_letters + string.digits, k=6))
            self.enc[key] = longUrl
            self.dec[longUrl] = key
        return self.base + self.dec[longUrl]

    def decode(self, shortUrl: str) -> str:
        return self.enc[shortUrl[len(self.base):]]

// Java
public class Codec {
    Map<String,String> enc = new HashMap<>(), dec = new HashMap<>();
    String base = "http://tinyurl.com/";
    public String encode(String longUrl) {
        if (!dec.containsKey(longUrl)) {
            String key = Integer.toHexString(longUrl.hashCode());
            enc.put(key, longUrl); dec.put(longUrl, key);
        }
        return base + dec.get(longUrl);
    }
    public String decode(String shortUrl) {
        return enc.get(shortUrl.substring(base.length()));
    }
}

// C++
class Codec {
    unordered_map<string,string> enc, dec;
    string base = "http://tinyurl.com/";
public:
    string encode(string longUrl) {
        if (!dec.count(longUrl)) {
            string key = to_string(hash<string>{}(longUrl));
            enc[key] = longUrl; dec[longUrl] = key;
        }
        return base + dec[longUrl];
    }
    string decode(string shortUrl) {
        return enc[shortUrl.substr(base.size())];
    }
};