URL shortener

Create an application (not web, in memory) that can handle:

1. Shortening of original URL by using provided SEO keyword. Keyword should be at max 20 symbols

Input: Original URL: https://blog.mysite.com/cool-article, Keyword: BEST-ARTICLE

Output: https://short.en/BEST-ARTICLE

2. Shortening of original URL, without provided keyword. Randomly generate 5 alpha-numeric keyword

Input: Original URL: https://blog.mysite.com/another-article

Output: https://short.en/Pq34r

3. Retrieve original URL by shorten URL

Input: https://short.en/Pq34r

Output: https://blog.mysite.com/another-article