> For the complete documentation index, see [llms.txt](https://nataliekung.gitbook.io/ladder_code/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nataliekung.gitbook.io/ladder_code/facebook/encode-and-decode-tinyurl.md).

# Encode and Decode TinyURL

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-%28-TinyURL-%29-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 the`encode`and`decode`methods for the TinyURL service. 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.

分析

1. string.ascii\_letters+string.digits 提供了可选的字符
2. ''.join(random.choice(chars) for \_ in range(6))得到了code
3. 2个map code2url 和url2code
4. encode时候有个while longURL not in url2code 保证了code重复情况下依然可以create新code

```
class Codec:
    alphabet = string.ascii_letters+string.digits
    code_base = "http://tinyurl.com/"

    def __init__(self):
        self.url2code = {}
        self.code2url = {}

    def encode(self, longUrl):
        """Encodes a URL to a shortened URL.

        :type longUrl: str
        :rtype: str
        """
        while longUrl not in self.url2code:
            code = ''.join(random.choice(self.alphabet) for _ in range(6))
            if code not in self.code2url:
                self.code2url[code] = longUrl
                self.url2code[longUrl] = code
        return self.code_base + code


    def decode(self, shortUrl):
        """Decodes a shortened URL to its original URL.

        :type shortUrl: str
        :rtype: str
        """
        return self.code2url[shortUrl[-6:]] 

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


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://nataliekung.gitbook.io/ladder_code/facebook/encode-and-decode-tinyurl.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.