|
| 1 | +#![feature(test)] |
| 2 | +#![expect(unstable_name_collisions)] |
| 3 | + |
| 4 | +use aoc::bitset::BitSet; |
| 5 | +use itertools::Itertools; |
| 6 | +use rustc_hash::FxHashMap; |
| 7 | + |
| 8 | +#[derive(Debug)] |
| 9 | +struct Input { |
| 10 | + graph: Vec<BitSet>, |
| 11 | + names: Vec<String>, |
| 12 | +} |
| 13 | + |
| 14 | +fn setup(input: &str) -> Input { |
| 15 | + let input = input.lines().map(|l| l.split('-').collect_tuple().unwrap()); |
| 16 | + |
| 17 | + let mut idx = FxHashMap::default(); |
| 18 | + for name in input.clone().flat_map(|(a, b)| [a, b]) { |
| 19 | + let i = idx.len(); |
| 20 | + idx.entry(name).or_insert(i); |
| 21 | + } |
| 22 | + |
| 23 | + let mut graph = vec![BitSet::new(); idx.len()]; |
| 24 | + for (a, b) in input.map(|(a, b)| (idx[a], idx[b])) { |
| 25 | + graph[a].insert(b); |
| 26 | + graph[b].insert(a); |
| 27 | + } |
| 28 | + |
| 29 | + let mut names = vec![String::new(); idx.len()]; |
| 30 | + for (name, i) in idx { |
| 31 | + names[i] = name.into(); |
| 32 | + } |
| 33 | + |
| 34 | + Input { graph, names } |
| 35 | +} |
| 36 | + |
| 37 | +fn max_bron_kerbosch(r: BitSet, mut p: BitSet, mut x: BitSet, graph: &[BitSet]) -> Option<BitSet> { |
| 38 | + if p.is_empty() && x.is_empty() { |
| 39 | + return Some(r); |
| 40 | + } |
| 41 | + |
| 42 | + let mut out = None::<BitSet>; |
| 43 | + let u = p.iter().chain(&x).next().unwrap(); |
| 44 | + for v in &(p.clone() - &graph[u]) { |
| 45 | + let mut r = r.clone(); |
| 46 | + r.insert(v); |
| 47 | + let n = &graph[v]; |
| 48 | + let result = max_bron_kerbosch(r, p.clone() & n, x.clone() & n, graph); |
| 49 | + if result.as_ref().map(|s| s.len()) > out.as_ref().map(|s| s.len()) { |
| 50 | + out = result; |
| 51 | + } |
| 52 | + p.remove(v); |
| 53 | + x.insert(v); |
| 54 | + } |
| 55 | + out |
| 56 | +} |
| 57 | + |
| 58 | +fn part1(input: &Input) -> usize { |
| 59 | + let t = &input |
| 60 | + .names |
| 61 | + .iter() |
| 62 | + .enumerate() |
| 63 | + .filter_map(|(i, name)| name.starts_with('t').then_some(i)) |
| 64 | + .collect::<BitSet>(); |
| 65 | + input |
| 66 | + .graph |
| 67 | + .iter() |
| 68 | + .enumerate() |
| 69 | + .flat_map(|(a, an)| { |
| 70 | + an.iter().take_while(move |&b| b < a).flat_map(move |b| { |
| 71 | + an.iter() |
| 72 | + .take_while(move |&c| c < b) |
| 73 | + .filter(move |&c| input.graph[b].contains(c)) |
| 74 | + .filter(move |&c| [a, b, c].into_iter().any(|i| t.contains(i))) |
| 75 | + }) |
| 76 | + }) |
| 77 | + .count() |
| 78 | +} |
| 79 | + |
| 80 | +fn part2(input: &Input) -> String { |
| 81 | + max_bron_kerbosch( |
| 82 | + Default::default(), |
| 83 | + (0..input.graph.len()).collect(), |
| 84 | + Default::default(), |
| 85 | + &input.graph, |
| 86 | + ) |
| 87 | + .unwrap() |
| 88 | + .into_iter() |
| 89 | + .map(|i| input.names[i].as_str()) |
| 90 | + .sorted_unstable() |
| 91 | + .intersperse(",") |
| 92 | + .collect() |
| 93 | +} |
| 94 | + |
| 95 | +aoc::main!(2024, 23, ex: 1); |
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