solution: day 16

data/examples/16.txt

@@ -0,0 +1,17 @@
+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################

src/bin/16.rs

@@ -0,0 +1,119 @@
+use std::{cmp::Reverse, collections::BinaryHeap};
+
+use aoc::grid_vec::{Direction, Grid, Point};
+use hashbrown::{HashMap, HashSet};
+
+fn parse_input(input: &str) -> (Grid, Point, Point) {
+    let mut grid: Grid = input.parse().unwrap();
+    let start = grid.find(b'S').unwrap();
+    let end = grid.find(b'E').unwrap();
+
+    grid[start] = b'.';
+    grid[end] = b'.';
+
+    (grid, start, end)
+}
+
+type Prev = HashMap<(Point, Direction), HashSet<(Point, Direction)>>;
+type Visited = HashMap<(Point, Direction), usize>;
+
+fn dijkstra(grid: &Grid, start: Point) -> (Visited, Prev) {
+    let mut prev: Prev = HashMap::new();
+    let mut visited: Visited = HashMap::new();
+
+    let mut bh = BinaryHeap::new();
+    bh.push(Reverse((0, start, Direction::EAST, start, Direction::EAST)));
+
+    while let Some(Reverse((len, loc, dir, ploc, pdir))) = bh.pop() {
+        let best = visited.entry((loc, dir)).or_insert(usize::MAX);
+
+        if len > *best {
+            continue;
+        }
+
+        prev.entry((loc, dir)).or_default().insert((ploc, pdir));
+
+        *best = len;
+
+        let n = loc + dir;
+
+        if grid.get(&n).filter(|&&c| c == b'.').is_some() && !visited.contains_key(&(n, dir)) {
+            bh.push(Reverse((len + 1, n, dir, loc, dir)));
+        }
+
+        let rl = dir.rotate_left();
+        if !visited.contains_key(&(loc, rl)) {
+            bh.push(Reverse((len + 1000, loc, rl, loc, dir)));
+        }
+
+        let rr = dir.rotate_right();
+        if !visited.contains_key(&(loc, rr)) {
+            bh.push(Reverse((len + 1000, loc, rr, loc, dir)));
+        }
+    }
+
+    (visited, prev)
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let (grid, start, end) = parse_input(input);
+    dijkstra(&grid, start)
+        .0
+        .into_iter()
+        .filter(|(k, _)| k.0 == end)
+        .map(|(_, v)| v)
+        .min()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let (grid, start, end) = parse_input(input);
+
+    let (visited, prev) = dijkstra(&grid, start);
+
+    let mut stack = Vec::new();
+    stack.push(
+        prev.keys()
+            .filter(|&&k| k.0 == end)
+            .min_by_key(|&k| visited.get(k))
+            .copied()
+            .unwrap(),
+    );
+
+    let mut visited = HashSet::new();
+    let mut seats = HashSet::new();
+
+    while let Some((loc, dir)) = stack.pop() {
+        if !visited.insert((loc, dir)) {
+            continue;
+        }
+
+        if let Some(prevs) = prev.get(&(loc, dir)) {
+            stack.extend(prevs);
+        }
+
+        seats.insert(loc);
+    }
+
+    seats.len().into()
+}
+
+aoc::solution!(16);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 16)),
+            Some(11048)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 16)),
+            Some(64)
+        );
+    }
+}

src/grid_vec/direction.rs

@@ -0,0 +1,45 @@
+use std::fmt::Display;
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
+pub struct Direction {
+    pub i: isize,
+    pub j: isize,
+}
+
+impl Display for Direction {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "({}, {})", self.i, self.j)
+    }
+}
+
+impl Direction {
+    pub const NORTH: Self = Direction { i: -1, j: 0 };
+    pub const EAST: Self = Direction { i: 0, j: 1 };
+    pub const SOUTH: Self = Direction { i: 1, j: 0 };
+    pub const WEST: Self = Direction { i: 0, j: -1 };
+
+    pub fn new(i: isize, j: isize) -> Self {
+        Self { i, j }
+    }
+
+    pub fn rotate_left(self) -> Self {
+        Self {
+            i: -self.j,
+            j: self.i,
+        }
+    }
+
+    pub fn rotate_right(self) -> Self {
+        Self {
+            i: self.j,
+            j: -self.i,
+        }
+    }
+}
+
+#[macro_export]
+macro_rules! dir {
+    ($i:literal, $j:literal) => {
+        Direction { i: $i, j: $j }
+    };
+}

src/grid_vec/grid.rs

@@ -0,0 +1,66 @@
+use std::{
+    fmt::Display,
+    ops::{Index, IndexMut},
+    str::FromStr,
+};
+
+use super::Point;
+
+#[derive(Debug, Clone)]
+pub struct Grid {
+    grid: Vec<Vec<u8>>,
+}
+
+impl FromStr for Grid {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let grid = s.lines().map(|x| x.as_bytes().to_vec()).collect();
+        Ok(Self { grid })
+    }
+}
+
+impl Display for Grid {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        for row in self.grid.iter() {
+            for cell in row.iter() {
+                write!(f, "{}", *cell as char)?;
+            }
+            writeln!(f)?;
+        }
+        Ok(())
+    }
+}
+
+impl Index<Point> for Grid {
+    type Output = u8;
+    fn index(&self, index: Point) -> &Self::Output {
+        &self.grid[index.i][index.j]
+    }
+}
+
+impl IndexMut<Point> for Grid {
+    fn index_mut(&mut self, index: Point) -> &mut Self::Output {
+        &mut self.grid[index.i][index.j]
+    }
+}
+
+impl Grid {
+    pub fn find(&self, f: u8) -> Option<Point> {
+        let (i, j, _) = self
+            .grid
+            .iter()
+            .enumerate()
+            .flat_map(|(i, x)| x.iter().copied().enumerate().map(move |(j, y)| (i, j, y)))
+            .find(|x| x.2 == f)?;
+
+        Some(Point::new(i, j))
+    }
+
+    pub fn get(&self, p: &Point) -> Option<&u8> {
+        self.grid.get(p.i).and_then(|r| r.get(p.j))
+    }
+
+    pub fn get_mut(&mut self, p: &Point) -> Option<&mut u8> {
+        self.grid.get_mut(p.i).and_then(|r| r.get_mut(p.j))
+    }
+}

src/grid_vec/mod.rs

@@ -0,0 +1,9 @@
+mod grid;
+mod direction;
+mod point;
+
+pub use grid::Grid;
+pub use direction::Direction;
+pub use point::Point;
+
+

src/grid_vec/point.rs

@@ -0,0 +1,91 @@
+use super::Direction;
+
+use std::{
+    fmt::Display,
+    ops::{Add, AddAssign},
+};
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
+pub struct Point {
+    pub i: usize,
+    pub j: usize,
+}
+
+impl Display for Point {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "({}, {})", self.i, self.j)
+    }
+}
+
+impl Add<Direction> for Point {
+    type Output = Self;
+    fn add(self, rhs: Direction) -> Self::Output {
+        Self {
+            i: self.i.wrapping_add(rhs.i as usize),
+            j: self.j.wrapping_add(rhs.j as usize),
+        }
+    }
+}
+
+impl AddAssign<Direction> for Point {
+    fn add_assign(&mut self, rhs: Direction) {
+        *self = *self + rhs
+    }
+}
+
+impl Point {
+    pub fn new(i: usize, j: usize) -> Self {
+        Self { i, j }
+    }
+
+    pub fn n(self) -> Self {
+        Self {
+            i: self.i.wrapping_sub(1),
+            j: self.j,
+        }
+    }
+
+    pub fn s(self) -> Self {
+        Self {
+            i: self.i.wrapping_add(1),
+            j: self.j,
+        }
+    }
+
+    pub fn e(self) -> Self {
+        Self {
+            i: self.i,
+            j: self.j.wrapping_sub(1),
+        }
+    }
+
+    pub fn w(self) -> Self {
+        Self {
+            i: self.i,
+            j: self.j.wrapping_add(1),
+        }
+    }
+
+    pub fn ne(self) -> Self {
+        self.n().e()
+    }
+
+    pub fn nw(self) -> Self {
+        self.n().w()
+    }
+
+    pub fn se(self) -> Self {
+        self.s().e()
+    }
+
+    pub fn sw(self) -> Self {
+        self.s().w()
+    }
+}
+
+#[macro_export]
+macro_rules! pnt {
+    ($i:literal, $j:literal) => {
+        Point { i: $i, j: $j }
+    };
+}

src/lib.rs

@@ -1,4 +1,5 @@
 #![feature(pattern)]
 
+pub mod grid_vec;
 pub mod parsers;
 pub mod template;