[2021] Day 12 part a

Author: connorslade

Cargo.lock

@@ -6,4 +6,6 @@ edition = "2021"
 [dependencies]
 common = { path = "../common" }
 hashbrown = "0.13.1"
+indoc = "2.0.4"
 nd_vec = "0.4.0"
+petgraph = "0.6.4"

aoc_2021/Cargo.toml

@@ -0,0 +1,145 @@
+use common::{Answer, Solution};
+use hashbrown::{HashMap, HashSet};
+use petgraph::graph::{NodeIndex, UnGraph};
+
+pub struct Day12;
+
+impl Solution for Day12 {
+    fn name(&self) -> &'static str {
+        "Passage Pathing"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let graph = parse(input);
+        paths_a(&graph, graph.start, HashSet::new()).into()
+    }
+
+    fn part_b(&self, _input: &str) -> Answer {
+        Answer::Unimplemented
+    }
+}
+
+fn paths_a<'a>(graph: &ParseResult<'a>, at: NodeIndex, mut visited: HashSet<NodeIndex>) -> usize {
+    if at == graph.end {
+        return 1;
+    }
+
+    if !visited.insert(at) && graph.graph[at].cave_type != Type::Big {
+        return 0;
+    }
+
+    graph
+        .graph
+        .neighbors(at)
+        .into_iter()
+        .map(|child| paths_a(graph, child, visited.clone()))
+        .sum()
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+enum Type {
+    Small,
+    Big,
+    Root,
+}
+
+struct Node<'a> {
+    name: &'a str,
+    cave_type: Type,
+}
+
+struct ParseResult<'a> {
+    graph: UnGraph<Node<'a>, ()>,
+    start: NodeIndex,
+    end: NodeIndex,
+}
+
+fn parse<'a>(input: &'a str) -> ParseResult<'a> {
+    let mut graph = UnGraph::new_undirected();
+    let mut nodes = HashMap::new();
+
+    fn make_node<'a>(name: &'a str) -> Node<'a> {
+        Node {
+            name,
+            cave_type: if name == "start" || name == "end" {
+                Type::Root
+            } else if name.chars().next().unwrap().is_uppercase() {
+                Type::Big
+            } else {
+                Type::Small
+            },
+        }
+    }
+
+    fn get_node<'a>(
+        nodes: &mut HashMap<&'a str, NodeIndex>,
+        graph: &mut UnGraph<Node<'a>, ()>,
+        name: &'a str,
+    ) -> NodeIndex {
+        *nodes
+            .entry(name)
+            .or_insert_with(|| graph.add_node(make_node(name)))
+    }
+
+    for line in input.lines() {
+        let (from, to) = line.split_once('-').unwrap();
+        let from = get_node(&mut nodes, &mut graph, from);
+        let to = get_node(&mut nodes, &mut graph, to);
+        graph.add_edge(from, to, ());
+    }
+
+    fn find<'a>(graph: &'a UnGraph<Node<'a>, ()>, name: &str) -> NodeIndex {
+        graph
+            .node_indices()
+            .find(|i| graph[*i].name == name)
+            .unwrap()
+    }
+
+    ParseResult {
+        start: find(&graph, "start"),
+        end: find(&graph, "end"),
+        graph,
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use common::Solution;
+    use indoc::indoc;
+
+    use super::Day12;
+
+    const CASE: &str = indoc! {"
+        start-A
+        start-b
+        A-c
+        A-b
+        b-d
+        A-end
+        b-end
+    "};
+
+    const CASE_2: &str = indoc! {"
+        dc-end
+        HN-start
+        start-kj
+        dc-start
+        dc-HN
+        LN-dc
+        HN-end
+        kj-sa
+        kj-HN
+        kj-dc
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day12.part_a(CASE), 10.into());
+        assert_eq!(Day12.part_a(CASE_2), 19.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day12.part_b(CASE), 36.into());
+    }
+}

aoc_2021/src/day_12.rs

@@ -1,4 +1,3 @@
-use common::DummySolution;
 pub use common::Solution;
 
 mod day_01;
@@ -12,11 +11,12 @@ mod day_08;
 mod day_09;
 mod day_10;
 mod day_11;
+mod day_12;
 mod day_13;
 mod day_14;
 // [import_marker]
 
-pub const ALL: [&dyn Solution; 14] = [
+pub const ALL: &[&dyn Solution] = &[
     &day_01::Day01,
     &day_02::Day02,
     &day_03::Day03,
@@ -28,8 +28,9 @@ pub const ALL: [&dyn Solution; 14] = [
     &day_09::Day09,
     &day_10::Day10,
     &day_11::Day11,
-    &DummySolution,
+    &day_12::Day12,
     &day_13::Day13,
     &day_14::Day14,
+    &day_12::Day12,
     // [list_marker]
 ];

aoc_2021/src/lib.rs

@@ -0,0 +1,27 @@
+# AOC 2021 Todo
+
+- [x] Day 1
+- [x] Day 2
+- [x] Day 3
+- [x] Day 4
+- [x] Day 5
+- [x] Day 6
+- [x] Day 7
+- [x] Day 8
+- [x] Day 9
+- [x] Day 10
+- [x] Day 11
+- [ ] Day 12
+- [x] Day 13
+- [x] Day 14
+- [ ] Day 15
+- [ ] Day 16
+- [ ] Day 17
+- [ ] Day 18
+- [ ] Day 19
+- [ ] Day 20
+- [ ] Day 21
+- [ ] Day 22
+- [ ] Day 23
+- [ ] Day 24
+- [ ] Day 25