day16

Cargo.lock

@@ -10,6 +10,7 @@ dependencies = [
  "aoc-runner-derive",
  "array2d",
  "itertools",
+ "prev-iter",
  "rust-crypto",
  "strum",
  "strum_macros",
@@ -95,6 +96,12 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "prev-iter"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ceacb352f798299b2044f4b9a894e8ef5d21115ccd293a323d44fc665132ec83"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.70"

Cargo.toml

@@ -14,3 +14,4 @@ itertools = "0.12.0"
 array2d = "0.3.0"
 strum = "0.25.0"
 strum_macros = "0.25"
+prev-iter = "0.1.2"

src/day15.rs

@@ -34,8 +34,6 @@ fn part2(input: &Vec<String>) -> usize {
             .try_into()
             .unwrap();
     for step in input {
-        
-        
         if let Some(dash) = step.find('-') {
             let label = &step[0..dash];
             let box_number = hash(label) as usize;

src/day16.rs

@@ -0,0 +1,211 @@
+use std::collections::{HashSet, VecDeque};
+use prev_iter::PrevPeekable;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+use strum_macros::Display;
+
+#[derive(Debug, Clone, Copy)]
+enum Tile {
+    None,
+    MirrorLeft,
+    MirrorRight,
+    SplitterVert,
+    SplitterHori
+}
+
+trait TileConvertable {
+    fn to_tile(&self) -> Tile;
+}
+
+impl TileConvertable for char {
+    fn to_tile(&self) -> Tile {
+        match self {
+            '.'  => Tile::None,
+            '/'  => Tile::MirrorLeft,
+            '\\' => Tile::MirrorRight,
+            '|'  => Tile::SplitterVert,
+            '-'  => Tile::SplitterHori,
+             _   => panic!("invalid tile char: {} AHHH", self)
+        }
+    }
+}
+
+
+#[aoc_generator(day16)]
+fn parse(input: &str) -> Vec<Vec<Tile>> {
+    let input = input.lines()
+        .map(|line| {
+            line.chars()
+                .map(|char| char.to_tile())
+                .collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>();
+
+    input
+}
+
+#[aoc(day16, part1)]
+fn part1(map: &Vec<Vec<Tile>>) -> usize {
+    let start = (Position{ x:0 , y:0}, Direction::Right);
+
+    trace_beams(start, map)
+}
+
+fn trace_beams((start_pos, start_dir): (Position, Direction), map: &Vec<Vec<Tile>>) -> usize {
+    let mut in_progress = VecDeque::from([(start_pos, start_dir)]);
+    let mut seen: HashSet<(Position, Direction)> = HashSet::new();
+
+    while !in_progress.is_empty() {
+        let mut cur = in_progress.pop_front();
+        while &cur != &None {
+            seen.insert(cur.clone().unwrap());
+            let (next, new_beam) = do_one_step(cur.clone().unwrap(), map);
+            if let Some(next) = next {
+                if !seen.contains(&next) {
+                    cur = Some(next);
+                } else {
+                    cur = None;
+                }
+            } else {
+                cur = None
+            }
+
+            if let Some(new_beam) = new_beam {
+                in_progress.push_back(new_beam);
+            }
+        }
+    }
+
+    seen.iter().map(|x| x.0).collect::<HashSet<_>>().len()
+}
+
+fn do_one_step(cur: (Position, Direction), map: &Vec<Vec<Tile>>) -> (Option<(Position, Direction)>, Option<(Position, Direction)>) {
+    let tile = map[cur.0.y as usize][cur.0.x as usize];
+    match tile {
+        Tile::None => (move_and_turn(&cur, None, map), None),
+        Tile::SplitterHori if {cur.1.is_hori()} => (move_and_turn(&cur, None, map), None),
+        Tile::SplitterVert if {cur.1.is_vert()} => (move_and_turn(&cur, None, map), None),
+        Tile::MirrorRight => (move_and_turn(&cur, if cur.1.is_hori() {Some(Direction::Right)} else {Some(Direction::Left)}, map), None),
+        Tile::MirrorLeft => (move_and_turn(&cur, if cur.1.is_hori() {Some(Direction::Left)} else {Some(Direction::Right)}, map), None),
+        Tile::SplitterVert => (move_and_turn(&cur, Some(Direction::Left), map), move_and_turn(&cur, Some(Direction::Right), map)),
+        Tile::SplitterHori => (move_and_turn(&cur, Some(Direction::Right), map), move_and_turn(&cur, Some(Direction::Left), map))
+    }
+}
+
+fn move_and_turn(cur: &(Position, Direction), turn: Option<Direction>, map: &Vec<Vec<Tile>>) -> Option<(Position, Direction)> {
+    let next_dir = if let Some(turn) = turn {cur.1.turn(turn)} else {cur.1};
+    let next_pos = cur.0.move_pos(next_dir);
+
+    if let Some(line) = map.get(next_pos.y as usize) {
+        if let Some(_) = line.get(next_pos.x as usize) {
+            return Some((next_pos, next_dir));
+        }
+    }
+
+    None
+}
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)]
+struct Position {
+    x: i32,
+    y: i32
+}
+
+impl Position {
+    fn move_pos(&self, dir: Direction) -> Position {
+        let (dx, dy) = match dir {
+            Direction::Up => (0, -1),
+            Direction::Down => (0, 1),
+            Direction::Left => (-1, 0),
+            Direction::Right => (1, 0),
+        };
+
+        return Position { x: self.x + dx, y: self.y + dy};
+    }
+}
+
+#[derive(Debug, Hash, PartialEq, Eq, Display, Copy, Clone)]
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right
+}
+
+impl Direction {
+    fn turn(&self, turn: Direction) -> Direction {
+        const TURN_ORDER: [Direction; 4] = [Direction::Up, Direction::Right, Direction::Down, Direction::Left];
+        let mut iter = PrevPeekable::new(TURN_ORDER.iter().cycle());
+        _ = iter.find(|dir| dir == &self).unwrap();
+
+        if turn == Direction::Left && *self == Direction::Up {
+            return Direction::Left;
+        }
+
+        let index = match turn {
+            Direction::Left => iter.prev(),
+            Direction::Right => iter.next(),
+            _ => panic!("Cannot turn {}", turn)
+        };
+
+        return *index.clone().unwrap();
+    }
+
+    fn is_hori(&self) -> bool {
+        [Direction::Right, Direction::Left].contains(self)
+    }
+
+    fn is_vert(&self) -> bool {
+        [Direction::Up, Direction::Down].contains(self)
+    }
+}
+
+
+
+#[aoc(day16, part2)]
+fn part2(map: &Vec<Vec<Tile>>) -> usize {
+    let x_size = map[0].len();
+    let y_size = map.len();
+    let mut edges = vec![];
+
+    let mut top = (0..x_size).map(|x| (Position{ x: x as i32, y: 0}, Direction::Down)).collect::<Vec<_>>();
+    let mut left = (0..y_size).map(|y| (Position{ x: 0, y: y as i32}, Direction::Right)).collect::<Vec<_>>();
+    let mut bottom = (0..x_size).map(|x| (Position{ x: x as i32, y: (y_size - 1) as i32}, Direction::Down)).collect::<Vec<_>>();
+    let mut right = (0..y_size).map(|y| (Position{ x: (x_size - 1) as i32, y: y as i32}, Direction::Left)).collect::<Vec<_>>();
+
+    edges.append(&mut top);
+    edges.append(&mut left);
+    edges.append(&mut bottom);
+    edges.append(&mut right);
+
+    let total = edges.iter().map(|x| trace_beams(*x, map)).collect::<Vec<_>>();
+
+    *total.iter().max().unwrap()
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EX: &str = r".|...\....
+|.-.\.....
+.....|-...
+........|.
+..........
+.........\
+..../.\\..
+.-.-/..|..
+.|....-|.\
+..//.|....";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 46);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EX)), 51);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day16;
 mod day15;
 mod day14;
 mod day13;