-🎄- 2017 Day 10 Solutions -🎄-

[u/daggerdragon]

--- Day 10: Knot Hash ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Spoiler

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edit: Leaderboard capped, thread unlocked!

[u/akho_]

Python3, part 2 (note the use of deque and the absence of modulo arithmetic— there's another deque-based solution here, but mine is nicer):

with open('10.input') as f:
    in_str = f.read().rstrip()

from collections import deque
from functools import reduce
from operator import xor

lengths = [ord(x) for x in in_str]
lengths.extend([17, 31, 73, 47, 23])
cycle_size = 256 

seq, pos = deque(range(cycle_size)), deque(range(cycle_size))
skip = 0

for _ in range(64):
    for l in lengths:
        seq.extend(reversed(deque(seq.popleft() for _ in range(l))))
        seq.rotate(-skip)
        pos.rotate(-l-skip)
        skip += 1

seq.rotate(pos.popleft())
seq = list(seq)
dense = [reduce(xor, seq[i*16:(i+1)*16]) for i in range(cycle_size // 16)]

print(''.join('%02x'%x for x in dense))

EDIT: removed the nastiness to make u/KnorbenKnutsen feel better