Encryption and decryption of 535 tinyurl

Directory links ：

Force buckle programming problem - The solution sums up _ Share + Record -CSDN Blog

GitHub Synchronous question brushing items ：

https://github.com/September26/java-algorithms

Original link ： Power button

describe ：

TinyURL It's a kind of URL Simplify services , such as ： When you enter a URL https://leetcode.com/problems/design-tinyurl  when , It will return a simplified URL http://tinyurl.com/4e9iAk . Please design a class to encrypt and decrypt TinyURL .

There is no limit to how encryption and decryption algorithms are designed and operated , You just need to guarantee one URL Can be encrypted into a TinyURL , And this TinyURL It can be restored to the original by decryption URL .

Realization Solution class ：

Solution() initialization TinyURL System object .
String encode(String longUrl) return longUrl Corresponding TinyURL .
String decode(String shortUrl) return shortUrl The original URL . The subject data guarantees a given shortUrl Is encrypted by the same system object .
 

Example ：

Input ：url = "https://leetcode.com/problems/design-tinyurl"
Output ："https://leetcode.com/problems/design-tinyurl"

explain ：
Solution obj = new Solution();
string tiny = obj.encode(url); // Returns the result of encryption TinyURL .
string ans = obj.decode(tiny); // Returns the original after decryption URL .
 

Tips ：

1 <= url.length <= 104
Topic data assurance url Is an effective URL

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/encode-and-decode-tinyurl
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Their thinking ：

*  Their thinking ：
*  Shorten the path , That can only form a mapping relationship , This mapping relationship is the mapping relationship between long links and short links .
*  There are many kinds of mapping relationships , I use the simplest one here , Long linked MD5 mapping .

Code ：

public class Solution535 {

    public static class Codec {
        Map<String, String> cache = new HashMap<>();

        // Encodes a URL to a shortened URL.
        public String encode(String longUrl) {
            String key = getMD5String(longUrl);
            cache.put(key, longUrl);
            return key;
        }

        // Decodes a shortened URL to its original URL.
        public String decode(String shortUrl) {
            return cache.get(shortUrl);
        }

        public String getMD5String(String str) {
            try {
                //  Generate a MD5 Encryption computing abstract 
                MessageDigest md = MessageDigest.getInstance("MD5");
                //  Calculation md5 function 
                md.update(str.getBytes());
                // digest() Finally, make sure to return to md5 hash value , The return value is 8 A string . because md5 hash The value is 16 Bit hex value , It's actually 8 A character 
                // BigInteger Function will 8 Bit string into 16 position hex value , To express in a string ; Get the string form of hash value 
                // One byte It's 8-bit binary , That is to say 2 Hexadecimal character （2 Of 8 The second power equals 16 Of 2 Power ）
                return new BigInteger(1, md.digest()).toString(16);
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }
    }

}