solution: day 23

data/examples/23.txt

@@ -0,0 +1,32 @@
+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

src/bin/23.rs

@@ -0,0 +1,88 @@
+use std::collections::BTreeSet;
+
+use hashbrown::{HashMap, HashSet};
+use itertools::Itertools;
+
+fn parse_graph(input: &str) -> HashMap<&str, BTreeSet<&str>> {
+    let nodes: HashSet<_> = input.lines().filter_map(|x| x.split_once('-')).collect();
+    let mut graph: HashMap<_, BTreeSet<_>> = HashMap::new();
+    for (n1, n2) in nodes.iter().copied() {
+        graph.entry(n1).or_default().insert(n2);
+        graph.entry(n2).or_default().insert(n1);
+    }
+
+    graph
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let graph = parse_graph(input);
+
+    let mut triples = HashSet::new();
+    for (n1, neigh) in graph.iter() {
+        for n2 in neigh.iter().copied() {
+            for n3 in graph[n2].iter() {
+                if graph[n3].contains(n1) && n1.starts_with('t') {
+                    let mut triple = [n1, n2, n3];
+                    triple.sort();
+                    triples.insert(triple);
+                }
+            }
+        }
+    }
+
+    triples.len().into()
+}
+
+pub fn part_two(input: &str) -> Option<String> {
+    let graph = parse_graph(input);
+
+    let p: BTreeSet<_> = graph.keys().copied().collect();
+    let r = HashSet::new();
+    let x = BTreeSet::new();
+
+    let mut maximals = HashSet::new();
+
+    let mut stack = Vec::new();
+    stack.push((r, p, x));
+
+    while let Some((r, mut p, mut x)) = stack.pop() {
+        if p.is_empty() && x.is_empty() {
+            let mut password = r.iter().copied().collect_vec();
+            password.sort();
+
+            maximals.insert(password.join(","));
+        }
+
+        while let Some(pp) = p.pop_last() {
+            let mut nr = r.clone();
+            nr.insert(pp);
+
+            let np = &p & &graph[pp];
+            let nx = &x & &graph[pp];
+
+            stack.push((nr, np, nx));
+
+            x.insert(pp);
+        }
+    }
+
+    maximals.into_iter().max_by_key(|x| x.len())
+}
+
+aoc::solution!(23);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 23)), Some(7));
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 23)),
+            Some("co,de,ka,ta".to_string())
+        );
+    }
+}