ah well, I tried switching to python's set() but it was slow because of the fact it is unordered. I would need to use a min() to find the minimum index number, which was slow af. indexing might be fast but pop(0) on a list is also just as fast.(switching to deque had no speed up either) The list operations I am using are mostly O(1) time

If I comment out this which does the adding:

# adds checksums
    part2_data = [y for x in part2_data for y in x]
    part2 = 0
    for i,x in enumerate(part2_data):
        if x != '.':
            part2 += i*x

so that it isolates the checksum part. it is still only 80-100ms. so the checksum part had no noticeable slowdown, even if I were to do the check sum at the same time I do the sorting it would not lower execution time.

so if I look at each part of my code. the first 4 lines will take 20 ms

input_data = input_data.replace('\r', '').replace('\n', '')
part2_data = [[i//2 for _ in range(int(x))] if i%2==0 else ['.' for _ in range(int(x))] for i,x in enumerate(input_data)]
part2_data = [ x for x in part2_data if x!= [] ]
part1_data = [y for x in part2_data for y in x]

The part1 for loop will take 10 ms.

The for loop to set up next_empty_slot_by_length will take another 10 ms.

The part2 for loop will take 10 ms, too!

and adding up the part2 checksums will add another 10 ms.

So, in total, it will do it in ~60 ms, but python startup overhead seems to add 20-40 ms depending if you are on Linux(20 ms) or Windows(40 ms). both are Host, not virtual. Linux usually has faster startup time.

I am not sure where I would see a speed up. It seems that the startup overhead makes this just slower than the other top performing solutions which are also hitting a limit of 40-60 ms.

no way, someone is able to do it in O(n) time with OCaml. absolutely nutty. lol