day(16): add solution

Signed-off-by: Matej Focko <me@mfocko.xyz>

samples/day16.txt

@@ -0,0 +1,10 @@
+.|...\....
+|.-.\.....
+.....|-...
+........|.
+..........
+.........\
+..../.\\..
+.-.-/..|..
+.|....-|.\
+..//.|....

src/bin/day16.rs

@@ -0,0 +1,122 @@
+use std::collections::VecDeque;
+
+use rayon::prelude::*;
+
+use aoc_2023::*;
+
+type Output1 = usize;
+type Output2 = Output1;
+
+type Position = Vector2D<isize>;
+
+fn direction(d: &Position) -> i32 {
+    match (d.x(), d.y()) {
+        (1, _) => 1,
+        (_, 1) => 2,
+        (-1, _) => 4,
+        (_, -1) => 8,
+        _ => unreachable!("invalid direction"),
+    }
+}
+
+fn next(c: char, d: Position) -> Vec<Position> {
+    match c {
+        '|' if d.x() != 0 => vec![Vector2D::new(0, 1), Vector2D::new(0, -1)],
+        '-' if d.y() != 0 => vec![Vector2D::new(1, 0), Vector2D::new(-1, 0)],
+        '/' => vec![Vector2D::new(-d.y(), -d.x())],
+        '\\' => vec![Vector2D::new(d.y(), d.x())],
+        _ => vec![d],
+    }
+}
+
+// fn draw_energized(map: &[Vec<i32>]) {
+//     let mut formatted = String::new();
+
+//     for row in map {
+//         for &c in row {
+//             formatted += if c != 0 { "#" } else { "." };
+//         }
+//         formatted += "\n";
+//     }
+
+//     debug!("Energized:\n{}", formatted);
+// }
+
+struct Day16 {
+    map: Vec<Vec<char>>,
+}
+
+impl Day16 {
+    fn solve(&self, start_pos: Position, start_dir: Position) -> usize {
+        let mut visited = vec![vec![0; self.map[0].len()]; self.map.len()];
+
+        let mut q: VecDeque<(Position, Position)> = VecDeque::new();
+        q.push_back((start_pos, start_dir));
+        visited[start_pos] |= direction(&start_dir);
+
+        while let Some((p, d)) = q.pop_front() {
+            for dp in next(self.map[p], d) {
+                if !in_range(&self.map, &(p + dp)) || visited[p + dp] & direction(&dp) != 0 {
+                    continue;
+                }
+
+                visited[p + dp] |= direction(&dp);
+                q.push_back((p + dp, dp));
+            }
+        }
+
+        // draw_energized(&visited);
+
+        visited
+            .iter()
+            .map(|row| row.iter().filter(|&&c| c != 0).count())
+            .sum()
+    }
+}
+
+impl Solution<Output1, Output2> for Day16 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        Self {
+            map: file_to_string(pathname)
+                .lines()
+                .map(|l| l.chars().collect())
+                .collect(),
+        }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.solve(Vector2D::new(0, 0), Vector2D::new(1, 0))
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        (0..self.map.len())
+            .into_par_iter()
+            .flat_map(|y| {
+                vec![
+                    (Vector2D::new(0, y as isize), Vector2D::new(1, 0)),
+                    (
+                        Vector2D::new(self.map[y].len() as isize - 1, y as isize),
+                        Vector2D::new(-1, 0),
+                    ),
+                ]
+            })
+            .chain((0..self.map[0].len()).into_par_iter().flat_map(|x| {
+                vec![
+                    (Vector2D::new(x as isize, 0), Vector2D::new(0, 1)),
+                    (
+                        Vector2D::new(x as isize, self.map.len() as isize - 1),
+                        Vector2D::new(0, -1),
+                    ),
+                ]
+            }))
+            .map(|(start_pos, start_dir)| self.solve(start_pos, start_dir))
+            .max()
+            .unwrap()
+    }
+}
+
+fn main() -> Result<()> {
+    Day16::main()
+}
+
+test_sample!(day_16, Day16, 46, 51);