#!/usr/bin/env python3 lines = (x.strip() for x in open("input.txt")) rules = {} def yield_rule(line, rule, depth): if len(rule) > 0: elem, *tail = rule for rest in check(line, elem, depth+1): yield from yield_rule(rest, tail, depth) else: yield line def check(line, idx, depth=0): if depth > 100: return rs = rules[idx] if isinstance(rs, str): if line.startswith(rs): yield line[len(rs):] else: for rule in rules[idx]: yield from yield_rule(line, rule, depth) sum = 0 for line in lines: line = '11: 42 31 | 42 11 31' if line.startswith('11:') else line line = '8: 42 | 42 8' if line.startswith('8:') else line if ":" in line: idx, r = line.split(": ") idx = int(idx) r = r[1:len(r)-1] if r.startswith('"') else [[int(num) for num in x.split()] for x in r.split(" | ")] rules[idx] = r elif line != "": for rest in check(line, 0): if rest == "": sum += 1 print(sum) exit(0)