力扣每日一题2022-06-29中等题：TinyURL的加密与解密

• • 题目描述
  • 思路
  • • 哈希表
    • • Python实现
      • Java实现
      • C++实现

TinyURL的加密与解密

根据题意，主要考察的是使用哈希表存储原url和新url的键值对关系，至于加密解密使用什么算法并没有要求。

K1, K2 = 1117, 10**9+7

class Codec:
    def __init__(self):
        self.map = {}
        self.urlToKey = {}

    def encode(self, longUrl: str) -> str:
        """Encodes a URL to a shortened URL.
        """
        if longUrl in self.urlToKey:
            return "http://tinyurl.com/" + str(self.urlToKey[longUrl])
        key, base = 0, 1
        for ch in longUrl:
            key = (key + ord(ch) * base) % K2
            base = (base * K1) % K2
        while key in self.map:
            key = (key+1) % K2
        self.map[key] = longUrl
        self.urlToKey[longUrl] = key
        return "http://tinyurl.com/" + str(key)

    def decode(self, shortUrl: str) -> str:
        """Decodes a shortened URL to its original URL.
        """
        i = shortUrl.rfind('/')
        key = int(shortUrl[i+1:])
        return self.map[key]
        

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

public class Codec {

    static final int K1 = 1117;
    static final int K2 = 1000000007;
    private Map dataBase = new HashMap();
    private Map urlToKey = new HashMap();

    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        if (urlToKey.containsKey(longUrl)) {
            return "http://tinyurl.com/" + urlToKey.get(longUrl);
        }
        int key = 0;
        long base = 1;
        for (int i = 0; i < longUrl.length(); i++) {
            char ch = longUrl.charAt(i);
            key = (int) ((key + (long) ch * base) % K2);
            base = (base * K1) % K2;
        }
        while (dataBase.containsKey(key)) {
            key = (key + 1) % K2;
        }
        dataBase.put(key, longUrl);
        urlToKey.put(longUrl, key);
        return "http://tinyurl.com/" + key;
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        int i = shortUrl.lastIndexOf("/") + 1;
        int key = Integer.parseInt(shortUrl.substring(i));
        return dataBase.get(key);
    }
}

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

const long long K1 = 1117;
const long long K2 = 1e9+7;

class Solution {
private:
    unordered_map dataBase;
    unordered_map urlToKey;

public:
    Solution() {

    }

    // Encodes a URL to a shortened URL.
    string encode(string longUrl) {
        if (urlToKey.count(longUrl) > 0) {
            return string("http://tinyurl.com/") + to_string(urlToKey[longUrl]);
        }
        long long key = 0, base = 1;
        for (auto c : longUrl) {
            key = (key + c * base) % K2;
            base = (base * K1) % K2;
        }
        while (dataBase.count(key) > 0) {
            key = (key + 1) % K2;
        }
        dataBase[key] = longUrl;
        urlToKey[longUrl] = key;
        return string("http://tinyurl.com/") + to_string(key);
    }

    // Decodes a shortened URL to its original URL.
    string decode(string shortUrl) {
        int i = shortUrl.rfind('/')+1;
        int key = stoi(shortUrl.substr(i, int(shortUrl.size()) - i));
        return dataBase[key];
    }
};

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