Advent_of_code/src/Year_2016/P7.py

# --- Day 7: Internet Protocol Version 7 ---

# While snooping around the local network of EBHQ, you compile a list of IP
# addresses (they're IPv7, of course; IPv6 is much too limited). You'd like to
# figure out which IPs support TLS (transport-layer snooping).

# An IP supports TLS if it has an Autonomous Bridge Bypass Annotation, or ABBA.
# An ABBA is any four-character sequence which consists of a pair of two
# different characters followed by the reverse of that pair, such as xyyx or
# abba. However, the IP also must not have an ABBA within any hypernet
# sequences, which are contained by square brackets.

# For example:

#     abba[mnop]qrst supports TLS (abba outside square brackets).
#     abcd[bddb]xyyx does not support TLS (bddb is within square brackets, even
# though xyyx is outside square brackets).
#     aaaa[qwer]tyui does not support TLS (aaaa is invalid; the interior
# characters must be different).
#     ioxxoj[asdfgh]zxcvbn supports TLS (oxxo is outside square brackets, even
# though it's within a larger string).

# How many IPs in your puzzle input support TLS?

import re

with open("files/P7.txt") as f:
    IPs = [
        re.split(r"\[([^\]]+)\]", line) for line in f.read().strip().split()
    ]


def abba(s: str) -> bool:
    for i0, i1, i2, i3 in zip(s, s[1:], s[2:], s[3:]):
        if i0 == i3 and i1 == i2 and i0 != i1:
            return True
    return False


def part_1() -> None:
    tls = 0
    for ip in IPs:
        sn, hn = (" ".join(ip[::2]), " ".join(ip[1::2]))
        if abba(sn) and not (abba(hn)):
            tls += 1

    print(f"There are {tls} IPs supporting TLS")


# --- Part Two ---

# You would also like to know which IPs support SSL (super-secret listening).

# An IP supports SSL if it has an Area-Broadcast Accessor, or ABA, anywhere in
# the supernet sequences (outside any square bracketed sections), and a
# corresponding Byte Allocation Block, or BAB, anywhere in the hypernet
# sequences. An ABA is any three-character sequence which consists of the same
# character twice with a different character between them, such as xyx or aba.
# A corresponding BAB is the same characters but in reversed positions: yxy and
# bab, respectively.

# For example:

#     aba[bab]xyz supports SSL (aba outside square brackets with corresponding
# bab within square brackets).
#     xyx[xyx]xyx does not support SSL (xyx, but no corresponding yxy).
#     aaa[kek]eke supports SSL (eke in supernet with corresponding kek in
# hypernet; the aaa sequence is not related, because the interior character
# must be different).
#     zazbz[bzb]cdb supports SSL (zaz has no corresponding aza, but zbz has a
# corresponding bzb, even though zaz and zbz overlap).

# How many IPs in your puzzle input support SSL?


def is_aba(s: str) -> list[str]:
    aba_list = []
    for i0, i1, i2 in zip(s, s[1:], s[2:]):
        if i0 == i2 and i0 != i1:
            aba_list.append("".join([i0, i1, i2]))
    return aba_list


def part_2() -> None:
    ssl = 0
    for ip in IPs:
        sn, hn = (" ".join(ip[::2]), " ".join(ip[1::2]))
        aba_list = is_aba(sn)
        for aba in aba_list:
            if aba[1] + aba[0] + aba[1] in hn:
                ssl += 1
                break

    print(f"There are {ssl} IPs supporting SSL")


if __name__ == "__main__":
    part_1()
    part_2()