day19.py

#!/usr/bin/env python3

import re
import sys

# sys.setrecursionlimit(10000)

src = open("input.txt", "r").readlines()
src = [r.strip() for r in src if r.strip()]

rules = {}
messages = []

for line in src:
    if line[0].isdigit():
        t = line.split(": ")
        n = int(t[0])

        if n == 8:
            t[1] = "42 | 42 8"
        if n == 11:
            t[1] = "42 31 | 42 11 31"

        r = t[1].replace('"', "")
        if r.isalpha():
            rules[n] = r
        else:
            rules[n] = []
            for rst in r.split(" | "):
                rules[n].append([int(x) for x in rst.split(" ")])
    else:
        messages.append(line)


def build(n, d):
    if d > 6:
        if n == 8:
            return "(please)"
        if n == 11:
            return "(stahp)"

    r = rules[n]
    if isinstance(r, str):
        return r

    p = []
    for rs in r:
        cs = ""
        for i in rs:
            cs += build(i, d + 1)
        p.append(cs)

    return "({})".format("|".join(p))


rxs = "^" + build(0, 0) + "$"
rx = re.compile(rxs)

c = 0
for m in messages:
    if rx.match(m):
        c += 1

print(c)