AOC 2020 day 16

aoc_2020_day16.py

import functools
import operator

with open('input.txt') as f:
    inp = f.read()

class Range:
    def __init__(self, lower, upper):
        self.lower = int(lower)
        self.upper = int(upper)

    def match(self, string):
        return self.lower <= int(string) <= self.upper

    def __repr__(self):
         return 'lower={0.lower} upper={0.upper}'.format(self)


class Rule:
    def __init__(self, string):
        x = string.split(': ')
        self.name = x[0]
        self.ranges = tuple(Range(*p.split('-')) for p in x[1].split(' or '))

    def match(self, string):
        return any(r.match(string) for r in self.ranges)

    def __repr__(self):
        return '<{0.name} ranges={0.ranges}>'.format(self)

rules = [*map(Rule, inp.split('\n\n')[0].splitlines())]

def find_invalid(s):
    for n in s.split(','):
        if not any(rule.match(n) for rule in rules):
            return n

other_tickets = inp.split('\n\n')[-1].splitlines()[1:]
print('part 1:', sum(map(int, filter(None, map(find_invalid, other_tickets)))))

valid_tickets = [t for t in other_tickets if find_invalid(t) is None]

num_fields = len(other_tickets[0].split(','))

fields = {}

for rule in rules:
    valid_fields = []
    fields[rule.name] = valid_fields
    for i in range(num_fields):
        a = map(lambda s: int(s.split(',')[i]), valid_tickets)
        if all(rule.match(n) for n in a):
            valid_fields.append(i)

# fields as tuples, sorted by number of valid fields
fat = [(k, v) for k, v in fields.items()]
fat.sort(key=lambda f: len(f[1]))


mapped = {k: None for k in range(num_fields)}

done = set()

for name, l in fat:
    n = (set(l) - done).pop()
    mapped[n] = name
    done.add(n)

my_ticket = {}
my_ticket_as_list = inp.split('\n\n')[1].splitlines()[-1].split(',')
for idx, v in mapped.items():
    my_ticket[v] = my_ticket_as_list[idx]

print('part 2:', functools.reduce(operator.mul, (int(v) for k, v in my_ticket.items() if k.startswith('departure'))))