# 0535. Encode and Decode TinyURL

<https://leetcode.com/problems/encode-and-decode-tinyurl>

## Description

> Note: This is a companion problem to the [System Design](https://leetcode.com/discuss/interview-question/system-design/) problem: [Design TinyURL](https://leetcode.com/discuss/interview-question/124658/Design-a-URL-Shortener-\(-TinyURL-\)-System/).

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 a class to encode a URL and decode a tiny URL.

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.

Implement the `Solution` class:

* `Solution()` Initializes the object of the system.
* `String encode(String longUrl)` Returns a tiny URL for the given `longUrl`.
* `String decode(String shortUrl)` Returns the original long URL for the given `shortUrl`. It is guaranteed that the given `shortUrl` was encoded by the same object.

**Example 1:**

```
**Input:** url = "https://leetcode.com/problems/design-tinyurl"
**Output:** "https://leetcode.com/problems/design-tinyurl"
**Explanation:**
Solution obj = new Solution();
string tiny = obj.encode(url); // returns the encoded tiny url.
string ans = obj.decode(tiny); // returns the original url after deconding it.
```

**Constraints:**

* `1 <= url.length <= 104`
* `url` is guranteed to be a valid URL.

## ac

```java
public class Codec {
    String prefix = "http://tinyurl.com/";
    String alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    Map<String, String> map = new HashMap<>();
    Random random = new Random();
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        String key = getCode();
        while (map.containsKey(key)) {
            key = getCode();
        }
        map.put(key, longUrl);
        return prefix+key;
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        return map.get(shortUrl.replace(prefix, ""));
    }

    private String getCode() {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 6; i++) {
            sb.append(alphabet.charAt(random.nextInt(62)));
        }
        return sb.toString();
    }
}

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



/*
3 ways: 1) simple counting; 2) hashCode(); 3) random of Alphabet, best.
*/
```