day 12

2021/src/day12.rs

@@ -0,0 +1,174 @@
+use std::collections::{HashMap, HashSet};
+use std::str::FromStr;
+
+use color_eyre::eyre;
+use eyre::eyre;
+
+use crate::lib::IterExt;
+
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+enum Size {
+    Big,
+    Small,
+}
+
+
+// this is a terrible way to do it, because it's completely tied to
+// the dataset and needs to be redone in order to e.g. use a sample
+// dataset. A better way would be to use [char; 2] to represent each
+// cave and supply a method that computes size from letter case.
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+#[allow(non_camel_case_types)]
+enum Tag {
+    start,
+    de,
+    DN,
+    jv,
+    MU,
+    oa,
+    OC,
+    rj,
+    vd,
+    VP,
+    WK,
+    yb,
+    end,
+}
+
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+struct Cave {
+    tag: Tag,
+    size: Size,
+}
+
+
+impl FromStr for Cave {
+    type Err = eyre::Report;
+    fn from_str(s: &str) -> eyre::Result<Self> {
+        let cave = match s {
+            "start" => Cave {tag: Tag::start, size: Size::Small},
+            "de" => Cave {tag: Tag::de, size: Size::Small},
+            "DN" => Cave {tag: Tag::DN, size: Size::Big},
+            "jv" => Cave {tag: Tag::jv, size: Size::Small},
+            "MU" => Cave {tag: Tag::MU, size: Size::Big},
+            "oa" => Cave {tag: Tag::oa, size: Size::Small},
+            "OC" => Cave {tag: Tag::OC, size: Size::Big},
+            "rj" => Cave {tag: Tag::rj, size: Size::Small},
+            "vd" => Cave {tag: Tag::vd, size: Size::Small},
+            "VP" => Cave {tag: Tag::VP, size: Size::Big},
+            "WK" => Cave {tag: Tag::WK, size: Size::Big},
+            "yb" => Cave {tag: Tag::yb, size: Size::Small},
+            "end" => Cave {tag: Tag::end, size: Size::Small},
+            _ => return Err(eyre!("Invalid cave tag: {}", s)),
+        };
+        Ok(cave)
+    }
+}
+
+
+type CaveMap = HashMap<Tag, Vec<Cave>>;
+
+
+struct Path {
+    order: Vec<Cave>,
+    visited: HashSet<Cave>,
+    doubled: Option<Cave>
+}
+
+impl Path {
+    fn new() -> Self {
+        Path {
+            order: vec![Cave {tag: Tag::start, size: Size::Small}],
+            visited: HashSet::new(),
+            doubled: None,
+        }
+    }
+
+    fn push(&mut self, cave: Cave) {
+        self.order.push(cave);
+        if cave.size == Size::Small {
+            let inserted = self.visited.insert(cave);
+            if !inserted { // value was already present in set
+                self.doubled = Some(cave);
+            }
+        }
+    }
+
+    fn pop(&mut self) {
+        let cave = self.order.pop().unwrap();
+        if cave.size == Size::Small {
+            match self.doubled {
+                Some(d) if d == cave => {self.doubled = None},
+                _ => {self.visited.remove(&cave);}
+            }
+        }
+    }
+
+    fn last(&self) -> Option<&Cave> {
+        self.order.last()
+    }
+}
+
+
+fn load(data: &str) -> eyre::Result<CaveMap> {
+    let mut map = HashMap::new();
+    for line in data.lines() {
+        let (a, b) = line.split('-').take_pair()?;
+        let cave_a = a.parse::<Cave>()?;
+        let cave_b = b.parse::<Cave>()?;
+
+        let neighbors_a = map.entry(cave_a.tag).or_insert_with(|| vec![]);
+        neighbors_a.push(cave_b);
+
+        let neighbors_b = map.entry(cave_b.tag).or_insert_with(|| vec![]);
+        neighbors_b.push(cave_a);
+    }
+    Ok(map)
+}
+
+
+fn can_visit_part1(path: &Path, cave: &Cave) -> bool {
+    if cave.size == Size::Big {true}
+    else if cave.tag == Tag::start {false}
+    else if path.visited.contains(cave) {false}
+    else {true}
+}
+
+fn can_visit_part2(path: &Path, cave: &Cave) -> bool {
+    if cave.size == Size::Big {true}
+    else if cave.tag == Tag::start {false}
+    else if path.visited.contains(cave) && path.doubled.is_some() {false}
+    else {true}
+}
+
+
+fn search<F>(map: &CaveMap, path: &mut Path, can_visit: F) -> Vec<Vec<Cave>> 
+where F: Fn(&Path, &Cave) -> bool + Copy
+{
+    let mut result = Vec::new();
+    for neighbor in &map[&path.last().unwrap().tag] {
+        if neighbor.tag == Tag::end {
+            path.push(*neighbor);
+            result.push(path.order.clone());
+            path.pop();
+        }
+        else if can_visit(path, neighbor) {
+            path.push(*neighbor);
+            let child_paths = search(map, path, can_visit);
+            result.extend(child_paths);
+            path.pop();
+        }
+    }
+    result
+}
+
+
+pub fn run(data: &str) -> eyre::Result<(usize, usize)> {
+    let map = load(data)?;
+    let one = search(&map, &mut Path::new(), can_visit_part1);
+    let two = search(&map, &mut Path::new(), can_visit_part2);
+
+    Ok((one.len(), two.len()))
+}

2021/src/lib.rs

@@ -133,9 +133,8 @@ impl Iterator for NeighborCoords {
         let row_offset = self.start_row + rel_row;
         let col_offset = self.start_col + rel_col;
         // the "neighbor window" is off by 1, so we make the comparisons off by 1 as well
-        if
-            (row_offset > 0 && row_offset <= self.num_rows
-            && col_offset > 0 && col_offset <= self.num_cols)
+        if row_offset > 0 && row_offset <= self.num_rows
+           && col_offset > 0 && col_offset <= self.num_cols
         {
             Some((row_offset - 1, col_offset - 1))
         }

2021/src/main.rs

@@ -4,14 +4,14 @@ use color_eyre::eyre;
 
 mod lib;
 use lib::load;
-mod day11;
+mod day12;
 
 
 fn main() -> eyre::Result<()> {
-    let data = load("data/11.txt")?;
+    let data = load("data/12.txt")?;
 
     let start = Instant::now();
-    let (one, two) = day11::run(&data)?;
+    let (one, two) = day12::run(&data)?;
     let (dur, unit) = format_ns(start.elapsed().as_nanos());
 
     let precision = 2.0 - dur.log10().floor();