535. Encode and Decode TinyURL - LeetCode

Question

535. Encode and Decode TinyURL

Solution

題目大意:實現長連接加密成短連接,短連接解密成長連接

思路:加密成短連接+key,將長連接按key保存到map,解密時根據短連接提取key,再從map中返回長連接

Java實現:

public class Codec {

    // https://leetcode.com/problems/design-tinyurl --> http://tinyurl.com/4e9iAk
    Map<Integer, String> map = new HashMap<>();
    int i = 0;
    
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        map.put(i, longUrl);
        return "http://tinyurl.com/" + (i++);
    }

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

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

Ref

https://leetcode.com/problems/encode-and-decode-tinyurl/discuss/100270/Three-different-approaches-in-java

Using simple counter

public class Codec {
    Map<Integer, String> map = new HashMap<>();
    int i=0;
    public String encode(String longUrl) {
        map.put(i,longUrl);
        return "http://tinyurl.com/"+i++;
    }
    public String decode(String shortUrl) {
        return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
    }
}

Using hashcode

public class Codec {
    Map<Integer, String> map = new HashMap<>();
    public String encode(String longUrl) {
        map.put(longUrl.hashCode(),longUrl);
        return "http://tinyurl.com/"+longUrl.hashCode();
    }
    public String decode(String shortUrl) {
        return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
    }
}

Using random function

public class Codec {
    Map<Integer, String> map = new HashMap<>();
    Random r=new Random();
    int key=r.nextInt(10000);
    public String encode(String longUrl) {
        while(map.containsKey(key))
            key= r.nextInt(10000);
        map.put(key,longUrl);
        return "http://tinyurl.com/"+key;
    }
    public String decode(String shortUrl) {
        return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
    }
}