leetcode

Encode and Decode TinyURL

记录一些Python3库的用法

  • alpha = string.ascii_letters + ‘0123456789’ # 静态属性
  • random.choice() # Choose a random element from a non-empty sequence

长url转短url，看大佬如何思考：StefanPochmann Two solutions and thoughts
若短连接用自增数字来设计会带来一些隐患：

  1. 安全，别人容易按数字遍历获取所有url
  2. 对某些数字敏感的人可能不会接受
  3. 同样长度的编码，纯数字的编码数量少于字母+数字组合的

leetcode 原题：

535. Encode and Decode TinyURL

Note: This is a companion problem to the System Design problem: Design TinyURL.
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.
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import random
import string


class Codec:
    alpha = string.ascii_letters + '0123456789'

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

    def encode(self, longUrl: str) -> str:
        """Encodes a URL to a shortened URL.
        """
        code = self.url2code.get(longUrl)
        while not code:
            code = ''.join(random.choice(Codec.alpha) for _ in range(6))
            if code in self.code2url:
                code = None
            else:
                self.url2code[longUrl] = code
                self.code2url[code] = longUrl
                return code
        return code

    def decode(self, shortUrl: str) -> str:
        """Decodes a shortened URL to its original URL.
        """
        return self.code2url[shortUrl]