aoc2017-day13-2

import sys

import re

def parse_firewalls(inputf):

return ([int(__)

for __ in _.split()]

for _ in

(re.sub("[:]", " ", _)

for _ in

(_.strip()

for _ in iter(inputf))

if _))

def scanner_pos(tick, depth):

x = depth - 1

return x - abs(x - tick % (2*x))

def positions(tick, firewalls):

return ((_, scanner_pos(tick + _[0], _[1])) for _ in firewalls)

def collisions(tick, firewalls, pos):

return ((f, p == pos) for f, p in positions(tick, firewalls) if p == pos)

def has_next(seq):

return next((True for _ in seq), False)

def gen_range(start, stop=None):

while stop == None or start < stop:

yield start

start += 1

def find_delay(firewalls, pos):

return next((_

for _, col in

((_, has_next(collisions(_, firewalls, pos)))

for _ in gen_range(0))

if not col),

None)

with sys.stdin as f:

firewalls = list(parse_firewalls(f))

print(find_delay(firewalls, 0))