import 'package:collection/collection.dart';
import 'package:more/more.dart';

SetMultimap<String, String> getNodes(List<String> lines) {
  var nodes = SetMultimap<String, String>();
  for (var l in lines) {
    var p = l.split('-');
    nodes[p.first].add(p.last);
    nodes[p.last].add(p.first);
  }
  return nodes;
}

part1(List<String> lines) {
  var nodes = getNodes(lines);
  var ts = nodes.keys.where((e) => e.startsWith('t'));
  var ret = <String>[];
  for (var t in ts) {
    ret.addAll(nodes[t]
        .combinations(2)
        .where((e) => nodes[e.first].contains(e.last))
        .map((e) => (([t] + e)..sort()).toString()));
  }
  return ret.toSet().length;
}

part2(List<String> lines) {
  var nodes = getNodes(lines);
  Iterable<Set<String>> useBK1(
      Set<String> R, Set<String> P, Set<String> X) sync* {
    if (P.isEmpty && X.isEmpty) {
      yield R;
      return;
    }
    for (var v in P.toSet()) {
      yield* useBK1(R.toSet()..add(v), P.intersection(nodes[v]),
          X.intersection(nodes[v]));
      P.remove(v);
      X.add(v);
    }
  }
  var vs = nodes.keys.toSet()..addAll(nodes.values.deepFlatten());
  var ret = useBK1({}, vs, {}).toList();
  var max = ret.map((e) => e.length).max;
  return ret.firstWhere((e) => e.length == max).sorted().join(',');
}

  

 rust

    
#[cfg(test)]
mod tests {
    use std::collections::HashMap;

    #[test]
    fn day23_part1_test() {
        let input = std::fs::read_to_string("src/input/day_23.txt").unwrap();
        let links = input
            .lines()
            .map(|l| l.split_once('-').unwrap())
            .collect::<Vec<(&str, &str)>>();

        let mut peer_map = HashMap::new();

        for pair in links {
            peer_map.entry(pair.0).or_insert(Vec::new()).push(pair.1);
            peer_map.entry(pair.1).or_insert(Vec::new()).push(pair.0);
        }

        let mut rings = vec![];
        for (pc, peers) in &peer_map {
            if !pc.starts_with('t') {
                continue;
            }
            for (i, first) in peers.iter().enumerate() {
                for second in peers[i..].iter() {
                    if first == second {
                        continue;
                    }
                    if !peer_map.get(first).unwrap().contains(second) {
                        continue;
                    }
                    let mut set = vec![pc, second, first];
                    set.sort();
                    if !rings.contains(&set) {
                        rings.push(set);
                    }
                }
            }
        }

        println!("{}", rings.len());
    }

    #[test]
    fn day23_part2_test() {
        let input = std::fs::read_to_string("src/input/day_23.txt").unwrap();
        let links = input
            .lines()
            .map(|l| l.split_once('-').unwrap())
            .collect::<Vec<(&str, &str)>>();

        let mut peer_map = HashMap::new();

        for pair in links {
            let p1 = peer_map.entry(pair.0).or_insert(Vec::new());
            if !p1.contains(&pair.1) {
                p1.push(pair.1);
            }
            let p2 = peer_map.entry(pair.1).or_insert(Vec::new());
            if !p2.contains(&pair.0) {
                p2.push(pair.0);
            }
        }

        let mut biggest_network = String::new();

        for (pc, peers) in &peer_map {
            let mut network = HashMap::new();
            network.insert(pc, peers.len());

            for first in peers {
                let mut total = 1;
                for second in peers.iter() {
                    if first == second {
                        continue;
                    }
                    if peer_map.get(first).unwrap().contains(second) {
                        total += 1;
                    }
                }
                network.insert(first, total);
            }

            let mut network_size = peers.len();
            loop {
                if network_size == 0 {
                    break;
                }
                let mut out = network
                    .iter()
                    .filter_map(|(k, v)| {
                        if v >= &network_size {
                            return Some(**k);
                        }
                        None
                    })
                    .collect::<Vec<_>>();
                if out.len() == network_size + 1 {
                    out.sort();
                    let pw = out.join(",");
                    // println!("{}", pw);
                    if pw.len() > biggest_network.len() {
                        biggest_network = pw;
                    }
                    break;
                }

                network_size -= 1;
            }
        }

        println!("{}", biggest_network);
    }
}

  

    
sub MAIN($input) {
    my $file = open $input;
    my @connection-list := $file.slurp.trim.lines>>.split("-")>>.List.List;

    my %connections;
    my %all-computers is SetHash;
    for @connection-list -> @c {
        my ($first, $second) = @c.sort;
        %connections{$first} = [] if %connections{$first}:!exists;
        %connections{$second} = [] if %connections{$second}:!exists;
        %connections{$first}.push($second);
        %all-computers{@c.all}++;
    }
    for %connections.values -> $list is rw {
        $list = $list.sort.List;
    }

    my $part1-solution = 0;
    for %connections.keys -> $c1 {
        for %connections{$c1}.Seq -> $c2 {
            for (%connections{$c1} ∩ %connections{$c2}).keys -> $c3 {
                next unless ($c1, $c2, $c3).any.substr(0,1) eq "t";
                $part1-solution++;
            }
        }
    }
    say "part1 solution: $part1-solution";

    my $part2-solution = find-max-party((), %connections, %all-computers).join(",");
    say "part2 solution: $part2-solution";
}

sub find-max-party(@party, %connections, %available-members) {
    my @max-party = @party;
    for %available-members.keys.sort -> $c1 {
        my @new-party := (|@party, $c1);
        my %new-available-members := %available-members ∩ %connections{$c1};
        my @max-party-candidate = find-max-party(@new-party, %connections, %new-available-members);
        @max-party = @max-party-candidate if @max-party-candidate.elems > @max-party.elems;
        last if @max-party.elems == @party.elems + %available-members.elems;
    }
    return @max-party;
}

  

    
import Data.Bifunctor
import Data.List
import Data.Ord
import Data.Set qualified as Set

views :: [a] -> [(a, [a])]
views [] = []
views (x : xs) = (x, xs) : (second (x :) <$> views xs)

choose :: Int -> [a] -> [[a]]
choose 0 _ = [[]]
choose _ [] = []
choose n (x : xs) = ((x :) <$> choose (n - 1) xs) ++ choose n xs

removeConnectedGroup connected = fmap (uncurry go . first Set.singleton) . Set.minView
  where
    go group hosts =
      maybe
        (group, hosts)
        (\h -> go (Set.insert h group) (Set.delete h hosts))
        $ find (flip all group . connected) hosts

main = do
  net <- Set.fromList . map (second tail . break (== '-')) . lines <$> readFile "input23"
  let hosts = Set.fromList $ [fst, snd] <*> Set.elems net
      connected a b = any (`Set.member` net) [(a, b), (b, a)]
      complete = all (uncurry $ all . connected) . views
  print
    . length
    . filter complete
    . filter (any ((== 't') . head))
    $ choose 3 (Set.elems hosts)
  putStrLn
    . (intercalate "," . Set.toAscList)
    . maximumBy (comparing Set.size)
    . unfoldr (removeConnectedGroup connected)
    $ hosts
``