--- Day 23: LAN Party ---

As The Historians wander around a secure area at Easter Bunny HQ, you come across posters for a LAN party scheduled for today! Maybe you can find it; you connect to a nearby datalink port and download a map of the local network (your puzzle input).

The network map provides a list of every connection between two computers. For example:

kh-tc
qp-kh
de-cg
ka-co
yn-aq
qp-ub
cg-tb
vc-aq
tb-ka
wh-tc
yn-cg
kh-ub
ta-co
de-co
tc-td
tb-wq
wh-td
ta-ka
td-qp
aq-cg
wq-ub
ub-vc
de-ta
wq-aq
wq-vc
wh-yn
ka-de
kh-ta
co-tc
wh-qp
tb-vc
td-yn
Each line of text in the network map represents a single connection; the line kh-tc represents a connection between the computer named kh and the computer named tc. Connections aren't directional; tc-kh would mean exactly the same thing.

LAN parties typically involve multiplayer games, so maybe you can locate it by finding groups of connected computers. Start by looking for sets of three computers where each computer in the set is connected to the other two computers.

In this example, there are 12 such sets of three inter-connected computers:

aq,cg,yn
aq,vc,wq
co,de,ka
co,de,ta
co,ka,ta
de,ka,ta
kh,qp,ub
qp,td,wh
tb,vc,wq
tc,td,wh
td,wh,yn
ub,vc,wq
If the Chief Historian is here, and he's at the LAN party, it would be best to know that right away. You're pretty sure his computer's name starts with t, so consider only sets of three computers where at least one computer's name starts with t. That narrows the list down to 7 sets of three inter-connected computers:

co,de,ta
co,ka,ta
de,ka,ta
qp,td,wh
tb,vc,wq
tc,td,wh
td,wh,yn
Find all the sets of three inter-connected computers. How many contain at least one computer with a name that starts with t?
def readfile():
    file_name = "23.txt" 

    mapping = {}
    with open(file_name) as f:
        tuples = [tuple(line.strip().split("-")) for line in f.readlines()]

        # Add reverse order as well
        tuples += [(i[1], i[0]) for i in tuples]

        # Map all computers to which they are connected
        for key, val in tuples:
            if key in mapping:
                mapping[key].append(val)
            else:
                mapping[key] = [val]

    return mapping


def make_mapping_part1(mapping, computer, depth, lan_party, lan_parties):
    # We have reached 3 computers so make sure that we have closed the loop
    if depth == 0:
        if lan_party[0] == lan_party[-1] and any(
            [i.startswith("t") for i in lan_party]
        ):
            lan_parties.add(tuple(sorted(lan_party[:3])))
        return

    # Check all computers that are connected to the current one
    for val in mapping[computer]:
        lan_party.append(val)
        make_mapping_part1(mapping, val, depth - 1, lan_party, lan_parties)
        del lan_party[-1]


def part1(mapping):
    lan_parties = set()
    # Find all lan parties with exactly 3 computers
    for computer in mapping:
        make_mapping_part1(mapping, computer, 3, [computer], lan_parties)

    print(len(lan_parties))

if __name__ == "__main__":
    test_file = False
    mapping = readfile()

    print("Answer to part 1:")
    part1(mapping)