day_19a.py

#!/usr/bin/python3

known_rules = dict()
subsections_of_rules = dict()
previously_seen_pairs = dict()


def DoesMsgFollowRule(message, source):
    if source in known_rules:
        if known_rules[source] == message:
            return True
        else:
            return False
    if (message, source) in previously_seen_pairs:
        return previously_seen_pairs[(message, source)]
    for subsection in subsections_of_rules[source]:
        parts = len(subsection)
        if parts == 1:
            if DoesMsgFollowRule(message, subsection[0]):
                previously_seen_pairs[(message, source)] = True
                return True
        elif parts == 2:
            for i in range(0, len(message) - 1):
                if DoesMsgFollowRule(
                    message[0 : i + 1], subsection[0]
                ) and DoesMsgFollowRule(message[i + 1 : len(message)], subsection[1]):
                    previously_seen_pairs[(message, source)] = True
                    return True
    previously_seen_pairs[(message, source)] = False
    return False


def main():
    file = open("../input/day_19_input")
    messages = list()
    for line in file:
        line = line.strip("\n")
        if line == "":
            continue
        index = line.find(":")
        if index != -1:
            rule_lhs = int(line[0:index])
            rule_rhs = line[index + 1 : len(line)]
            if rule_lhs in known_rules:
                rule_rhs = known_rules[lhs]
            index = rule_rhs.find('"')
            if index != -1:
                known_rules[rule_lhs] = rule_rhs[index + 1]
            else:
                rule_subsection = list()
                num_in_rule_section = 0
                for c in rule_rhs:
                    if c == " ":
                        if num_in_rule_section > 0:
                            rule_subsection.append(num_in_rule_section)
                        num_in_rule_section = 0
                    elif c == "|":
                        if rule_lhs not in subsections_of_rules:
                            subsections_of_rules[rule_lhs] = list()
                        subsections_of_rules[rule_lhs].append(rule_subsection)
                        rule_subsection = list()
                    else:
                        num_in_rule_section = 10 * num_in_rule_section + int(c)
                rule_subsection.append(num_in_rule_section)
                if rule_lhs not in subsections_of_rules:
                    subsections_of_rules[rule_lhs] = list()
                subsections_of_rules[rule_lhs].append(rule_subsection)
        else:
            messages.append(line)
    res = 0
    for message in messages:
        if DoesMsgFollowRule(message, 0):
            res += 1
        previously_seen_pairs.clear()
    print(res)
    return 0


if __name__ == "__main__":
    main()