url-shortener.py

"""
#55
Microsoft

This problem was asked by Microsoft.

Implement a URL shortener with the following methods:

shorten(url), which shortens the url into a six-character alphanumeric string, such as zLg6wl.
restore(short), which expands the shortened string into the original url. If no such shortened string exists, return null.

Hint: What if we enter the same URL twice?

"""
import secrets

URLDict = dict()
alphabets = "abcdefghijklmnopqrstuvwxyz"
numbers = "0123456789"
alnum = list(alphabets+alphabets.upper()+numbers)

def createShortURL():
    shortURL = ""
    while shortURL == "":
        while len(shortURL) < 6:
            shortURL += secrets.SystemRandom().choice(alnum)
        if shortURL in URLDict.keys():
            shortURL = ""
    return shortURL

def shortenNonRedundant(newLongURL):
    for shortURL in URLDict.keys():
        if URLDict[shortURL] == newLongURL:
            return shortURL
    newShortURL = createShortURL()
    URLDict[newShortURL] = newLongURL
    return newShortURL

def shortenRedundant(newLongURL):
    newShortURL = createShortURL()
    URLDict[newShortURL] = newLongURL
    return newShortURL

def restore(shortURL):
    if shortURL in URLDict.keys():
        return URLDict[shortURL]
    else:
        return None

def main():
    URLs = ["www.facebook.com", "www.google.com", "www.facebook.com"]

    print("Non-redundant Shortening:")
    for URL in URLs:
        shortURL = shortenNonRedundant(URL)
        print(shortURL,"-",restore(shortURL))
    
    print("\nRedundant Shortening:")
    for URL in URLs:
        shortURL = shortenRedundant(URL)
        print(shortURL,"-",restore(shortURL))

if __name__ == "__main__":
    main()