Advent of code 2020, Day 16, Python3.9

day16.py

from sys import stdin
from re import findall
from collections import defaultdict
from functools import reduce
import operator

parts = [[findall('\d+', l)
          for l in x.split('\n')]
          for x in stdin.read().split('\n\n')]
rules = [[[int(r[i]),int(r[i+1])]
          for i in range(0,len(r),2)]
         for r in parts[0]]
ticket = [int(n) for n in parts[1][1]]
nearby = [[int(n) for n in t] for t in parts[2][1:] if t]

# Part 1
bad = [
    x for x in (int(n) for t in nearby for n in t)
    if not any(r[0]<=x<=r[1]
               for r in (r for sr in rules for r in sr))]
print (sum(bad))

# Part 2
matches = defaultdict(list)
for i,col in enumerate(zip(*(t for t in nearby
                             if all(x not in bad for x in t)))):
    for j,rule in enumerate(rules):
        if all(any(r[0]<=x<=r[1] for r in rule) for x in col):
            matches[j].append(i)
mapping = {}
for i in sorted(matches, key=lambda x: len(matches[x])):
    mapping[next(x for x in matches[i] if x not in mapping)] = i
print(reduce(operator.mul,
             (ticket[i] for i,j in mapping.items() if j<6), 1))