Complete day 25

Cargo.toml

@@ -33,4 +33,5 @@ regex = "1.10.2"
 num = "0.4.1"
 itertools = "0.12.0"
 colored = "2.1.0"
-z3 = "0.12"
+rand = "0.8.5"
+z3 = "0.12" # only works on Linux

data/examples/25.txt

@@ -0,0 +1,13 @@
+jqt: rhn xhk nvd
+rsh: frs pzl lsr
+xhk: hfx
+cmg: qnr nvd lhk bvb
+rhn: xhk bvb hfx
+bvb: xhk hfx
+pzl: lsr hfx nvd
+qnr: nvd
+ntq: jqt hfx bvb xhk
+nvd: lhk
+lsr: lhk
+rzs: qnr cmg lsr rsh
+frs: qnr lhk lsr

src/bin/25.rs

@@ -0,0 +1,97 @@
+use std::collections::{HashMap, HashSet};
+
+advent_of_code::solution!(25);
+
+type Graph = HashMap<String, Vec<String>>;
+
+fn parse(input: &str) -> Graph {
+    let mut graph: Graph = HashMap::new();
+    for line in input.lines() {
+        let mut parts = line.split(": ");
+        let key = parts.next().unwrap();
+        let values: Vec<String> = parts
+            .next()
+            .unwrap()
+            .split_whitespace()
+            .map(|s| s.to_string())
+            .collect();
+
+        for value in &values {
+            graph
+                .entry(value.clone())
+                .or_insert(vec![])
+                .push(key.to_string());
+            graph
+                .entry(key.to_string())
+                .or_insert(vec![])
+                .push(value.clone());
+        }
+    }
+
+    graph
+}
+
+fn find_left_size(graph: &Graph) -> u32 {
+    let start = graph.keys().next().unwrap();
+    let mut component = HashSet::from([start.to_string()]);
+
+    let mut middle_edges = graph[start]
+        .iter()
+        .map(|end| (start.to_string(), end.to_string()))
+        .collect::<HashSet<_>>();
+
+    while middle_edges.len() > 3 {
+        let next = middle_edges
+            .iter()
+            .cloned()
+            .map(|(_start, end)| end)
+            .min_by_key(|end| {
+                graph[end]
+                    .iter()
+                    .filter(|node| !component.contains(*node))
+                    .count()
+            })
+            .unwrap();
+
+        component.insert(next.to_string());
+
+        for neighbour in &graph[&next] {
+            if component.contains(neighbour) {
+                middle_edges.remove(&(neighbour.to_string(), next.to_string()));
+            } else {
+                middle_edges.insert((next.to_string(), neighbour.to_string()));
+            }
+        }
+    }
+
+    component.len() as u32
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let graph = parse(input);
+
+    let left_size = find_left_size(&graph);
+
+    Some(left_size * (graph.len() as u32 - left_size))
+}
+
+pub fn part_two(_: &str) -> Option<u32> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(54));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}