# 535. Encode and Decode TinyURL

#### Medium

***

> 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.

```
class Codec:
    def __init__(self):
        self.db = {}
        self.MOD = 10**9

    def encode(self, longUrl: str) -> str:
        """Encodes a URL to a shortened URL.
        """
        val = 0
        for index,char in enumerate(list(longUrl)):
            val += ord(char)*index
        val = val % self.MOD
        val = str(val)
        self.db[val] = longUrl
        return val
        

    def decode(self, shortUrl: str) -> str:
        """Decodes a shortened URL to its original URL.
        """
        return self.db[shortUrl]
        

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