I just wanted to solve it with O(len(str(start)) + len(str(end))) time complexity, since there is a more advanced version of the same kata where a standard for-loop that checks each integer from start to end won't fit into the time limit. Hence the code complexity and size. It does feel like creating a masterpiece though: it was a very meticulous work, which took me one full evening. But I love the result.

Took me more time than I thought it would, but enjoyed it. Kudos to the author.

ditto. I also targeted a wrong format. Besides, I think this kata should be moved to the 7 kyu category at least.

There should be one more condition added on the 0 and negative values being unacceptable. I though it was implied, and ran into a couple issues. Either add such cases to the testing pool and the description, or do not accept negative values. How can a valid size be negative?

challenging, but such a relief when it finally resolved all the tests. I would rate this kata higher than 6: even though the final solution is simple, it takes some time to arrive at it.

I'd suggest googling "Code complexity" or "Big O notation". There are tons of youtube videos on the matter as well. I would publish a youtube link here, but I doubt it's allowed.

My bad. I was just checking how my breadcrumb URL generator looks in HTML (it's another kata), so I thought I would write a comment to a random kata to review its format and then delete it. But now you responded to it, so I can't delete it any longer. :D Sorry for the confusuon again

The test case comparison only works when the outcome of your function is a string. In your case it is a 'NonType' object. Since "NoneType" object doesn't have certain attributes (e.g.: it doesn't have 'replace' attribute), the evaluator fails to run the test case comparison.

In a nutshell, please make sure your function returns a string

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