Again Elves are back. This time a problem was not that hard to solve but still was time consuming as previous versions. I again took help from reddit thread, specially from here.
def rule_maker(raw_rules): rules = {} for rule in raw_rules: key, value = rule.split(': ') if value[0] == '"': rules[int(key)] = value[1:-1] else: values = value.split(' | ') temp_v = [] for v in values: temp_v.append([int(vv) for vv in v.split(' ')]) rules[int(key)] = temp_v return rules def match_rule(expr, stack): if len(stack) > len(expr): return False elif len(stack) == 0 or len(expr) == 0: return len(stack) == 0 and len(expr) == 0 c = stack.pop() if isinstance(c, str): if expr[0] == c: return match_rule(expr[1:], stack.copy()) else: for rule in rules[c]: if match_rule(expr, stack + list(reversed(rule))): return True return False def count_messages(rules, messages): total = 0 for message in messages: if match_rule(message, list(reversed(rules[0][0]))): total += 1 return total with open("day19.txt") as fp: raw_rules, message = fp.read().split('\n\n') raw_rules = raw_rules.splitlines() message = message.splitlines() rules = rule_maker(raw_rules) print(f"Part 1: {count_messages(rules, message)}") rules[8] = [[42], [42, 8]] rules[11] = [[42, 31], [42, 11, 31]] print(f"Part 2: {count_messages(rules, message)}") # rules[0] 
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