535. Encode and Decode TinyURL(rand and srand)

Note: This is a companion problem to the System Design problem: Design 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.

Approach #1: C++.

class Solution {
public:

    // Encodes a URL to a shortened URL.
    string encode(string longUrl) {
        if (longToTiny.count(longUrl)) return baseUrl + longToTiny[longUrl];
        string tinyString = "";
        do {
            for (int i = 0; i < 6; ++i) {
                //srand((unsigned)time(0));
                int index = rand() % characters.length();
                tinyString += characters[index];
            }    
        } while (longToTiny.count(tinyString));
        
        longToTiny[longUrl] = tinyString;
        tinyToLong[baseUrl+tinyString] = longUrl;
        
        return baseUrl + tinyString;
    }

    // Decodes a shortened URL to its original URL.
    string decode(string shortUrl) {
        return tinyToLong[shortUrl];
    }
    
private:
    string baseUrl = "http://www.leetcode.com/";
    string characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
    unordered_map<string, string> longToTiny;
    unordered_map<string, string> tinyToLong;
};

// Your Solution object will be instantiated and called as such:
// Solution solution;
// solution.decode(solution.encode(url));

　　

Approach #2: Python.

class Codec:
    alphabet = string.ascii_letters + '0123456789'
    
    def __init__(self):
        self.url2code = {}
        self.code2url = {}

    def encode(self, longUrl):
        """Encodes a URL to a shortened URL.
        
        :type longUrl: str
        :rtype: str
        """
        while longUrl not in self.url2code:
            code = ''.join(random.choice(Codec.alphabet) for _ in range(6))
            if code not in self.code2url:
                self.code2url[code] = longUrl
                self.url2code[longUrl] = code
        return 'http://tinyurl.com/' + self.url2code[longUrl]
        

    def decode(self, shortUrl):
        """Decodes a shortened URL to its original URL.
        
        :type shortUrl: str
        :rtype: str
        """
        return self.code2url[shortUrl[-6:]]
        

# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.decode(codec.encode(url))

　　

Time Submitted	Status	Runtime	Language
a few seconds ago	Accepted	28 ms	python
2 minutes ago	Accepted	36 ms	python
13 minutes ago	Accepted	8 ms	cpp