Implement day 12 part 1

2021/src/day12.rs

@@ -1,9 +1,81 @@
+use std::collections::HashMap;
 use std::io::Read;
 
-pub fn part1(_input: &mut dyn Read) -> String {
-    todo!()
+use crate::common::LineIter;
+
+type EdgeMap = HashMap<String, Vec<String>>;
+
+fn read_edges(input: &mut dyn Read) -> EdgeMap {
+    let mut reader = LineIter::new(input);
+    let mut edges = EdgeMap::new();
+
+    while let Some(line) = reader.next() {
+        let (from, to) = line.split_once('-').unwrap();
+
+        edges
+            .entry(from.to_owned())
+            .or_default()
+            .push(to.to_owned());
+
+        edges
+            .entry(to.to_owned())
+            .or_default()
+            .push(from.to_owned());
+    }
+
+    edges
+}
+
+fn is_small(cave: &str) -> bool {
+    cave.chars().all(|c| c.is_ascii_lowercase())
+}
+
+fn dfs_routes<'a>(edges: &'a EdgeMap, route: &'_ mut Vec<&'a str>, pos: &'a str) -> usize {
+    if is_small(pos) && route.contains(&pos) {
+        return 0;
+    }
+
+    if pos == "end" {
+        return 1;
+    }
+
+    route.push(pos);
+
+    let routes = edges[pos]
+        .iter()
+        .map(|new_pos| dfs_routes(edges, route, new_pos))
+        .sum();
+
+    route.pop();
+
+    routes
+}
+
+pub fn part1(input: &mut dyn Read) -> String {
+    let edges = read_edges(input);
+    let mut route = Vec::new();
+
+    dfs_routes(&edges, &mut route, "start").to_string()
 }
 
 pub fn part2(_input: &mut dyn Read) -> String {
     todo!()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::test_implementation;
+
+    const SAMPLE1: &[u8] = include_bytes!("samples/12.1.txt");
+    const SAMPLE2: &[u8] = include_bytes!("samples/12.2.txt");
+    const SAMPLE3: &[u8] = include_bytes!("samples/12.3.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation(part1, SAMPLE1, 10);
+        test_implementation(part1, SAMPLE2, 19);
+        test_implementation(part1, SAMPLE3, 226);
+    }
+}