day 16 part 2

day 16 part 1

src/day16.rs

@@ -0,0 +1,160 @@
+use std::{
+    collections::{BinaryHeap, HashMap},
+    fs::read_to_string,
+};
+
+use itertools::Itertools;
+
+use crate::utils::grid::{Coord, Grid};
+
+pub fn day_main() {
+    let input = read_to_string("input/day16.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+enum Dir {
+    N,
+    E,
+    S,
+    W,
+}
+
+impl Dir {
+    fn nexts(&self) -> [Self; 2] {
+        match self {
+            Dir::N | Dir::S => [Dir::W, Dir::E],
+            Dir::E | Dir::W => [Dir::S, Dir::N],
+        }
+    }
+}
+
+struct Step(Coord, Dir, usize, Vec<Coord>);
+
+impl Ord for Step {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        other.2.cmp(&self.2)
+    }
+}
+impl PartialOrd for Step {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+impl PartialEq for Step {
+    fn eq(&self, other: &Self) -> bool {
+        other.2.eq(&self.2)
+    }
+}
+impl Eq for Step {}
+
+fn part1(input: &str) -> RiddleResult {
+    use Dir::*;
+    let maze = Grid::parse(input);
+    let start = maze.entries().find(|(_p, c)| **c == 'S').unwrap().0;
+    let end = maze.entries().find(|(_p, c)| **c == 'E').unwrap().0;
+    let mut visited = HashMap::<(Coord, Dir), usize>::new();
+    let mut stack: BinaryHeap<Step> = BinaryHeap::new();
+    stack.push(Step(start, E, 0, vec![]));
+    while let Some(Step(np, nd, cost, _)) = stack.pop() {
+        if visited.contains_key(&(np, nd)) {
+            continue;
+        }
+        visited.insert((np, nd), cost);
+        if np == end {
+            return cost;
+        }
+        for d in nd.nexts() {
+            if !visited.contains_key(&(np, d)) {
+                stack.push(Step(np, d, cost + 1000, vec![]));
+            }
+        }
+        let forward = match nd {
+            N => (np.0, np.1 - 1),
+            E => (np.0 + 1, np.1),
+            S => (np.0, np.1 + 1),
+            W => (np.0 - 1, np.1),
+        };
+        if maze[forward] != '#' && !visited.contains_key(&(forward, nd)) {
+            stack.push(Step(forward, nd, cost + 1, vec![]));
+        }
+    }
+    panic!("no path found")
+}
+
+fn part2(input: &str) -> RiddleResult {
+    use Dir::*;
+    let maze = Grid::parse(input);
+    let start = maze.entries().find(|(_p, c)| **c == 'S').unwrap().0;
+    let end = maze.entries().find(|(_p, c)| **c == 'E').unwrap().0;
+    let mut visited = HashMap::<(Coord, Dir), usize>::new();
+    let mut stack: BinaryHeap<Step> = BinaryHeap::new();
+    stack.push(Step(start, E, 0, vec![]));
+
+    let mut best: Option<usize> = None;
+    let mut visited_by_best: Vec<Coord> = vec![start, end];
+    while let Some(Step(np, nd, cost, mut pred)) = stack.pop() {
+        if let Some(b) = best {
+            if b < cost {
+                break; // can't reach the end point with best cost anymore
+            }
+        }
+        visited.insert((np, nd), cost);
+        if np == end {
+            best = Some(cost);
+            visited_by_best.append(&mut pred);
+        }
+        pred.push(np);
+        for d in nd.nexts() {
+            if !visited.contains_key(&(np, d)) {
+                stack.push(Step(np, d, cost + 1000, pred.clone()));
+            }
+        }
+        let forward = match nd {
+            N => (np.0, np.1 - 1),
+            E => (np.0 + 1, np.1),
+            S => (np.0, np.1 + 1),
+            W => (np.0 - 1, np.1),
+        };
+        if maze[forward] != '#' && !visited.contains_key(&(forward, nd)) {
+            stack.push(Step(forward, nd, cost + 1, pred));
+        }
+    }
+    visited_by_best.into_iter().unique().count()
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 7036);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 45);
+    }
+}

src/lib.rs

@@ -13,5 +13,6 @@ pub mod day12;
 pub mod day13;
 pub mod day14;
 pub mod day15;
+pub mod day16;
 // PLACEHOLDER
 pub mod utils;

src/main.rs

@@ -20,6 +20,7 @@ fn main() {
         (13, day13::day_main),
         (14, day14::day_main),
         (15, day15::day_main),
+        (16, day16::day_main),
         // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());