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.

I was just watching, but I was shocked when I saw it, it's just something!