From 15fccb9f5ed31e2e85aeffae69390145166ba941 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Sun, 17 Dec 2023 18:09:44 +0100
Subject: [PATCH] day(17): add solution

Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 samples/day17.txt |  13 +++++
 src/bin/day17.rs  | 135 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 148 insertions(+)
 create mode 100644 samples/day17.txt
 create mode 100644 src/bin/day17.rs

diff --git a/samples/day17.txt b/samples/day17.txt
new file mode 100644
index 0000000..f400d6e
--- /dev/null
+++ b/samples/day17.txt
@@ -0,0 +1,13 @@
+2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533
diff --git a/src/bin/day17.rs b/src/bin/day17.rs
new file mode 100644
index 0000000..8e7457f
--- /dev/null
+++ b/src/bin/day17.rs
@@ -0,0 +1,135 @@
+use std::collections::HashSet;
+
+use aoc_2023::*;
+
+type Output1 = u32;
+type Output2 = Output1;
+
+fn left(v: &Vector2D<isize>) -> Vector2D<isize> {
+    Vector2D::new(v.y(), -v.x())
+}
+
+fn right(v: &Vector2D<isize>) -> Vector2D<isize> {
+    Vector2D::new(-v.y(), v.x())
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct State {
+    heat_loss: u32,
+    distance: isize,
+    position: Vector2D<isize>,
+    direction: Vector2D<isize>,
+}
+
+impl State {
+    fn step(&self, m: &[Vec<u32>], direction: Vector2D<isize>, steps: isize) -> State {
+        let position = self.position + (direction * steps);
+        let distance = self.distance + steps;
+        let heat_loss = self.heat_loss
+            + (1..=steps)
+                .map(|s| m[self.position + direction * s])
+                .sum::<u32>();
+
+        State {
+            heat_loss,
+            distance,
+            position,
+            direction,
+        }
+    }
+}
+
+struct Day17 {
+    map: Vec<Vec<u32>>,
+}
+
+impl Day17 {
+    fn astar(&self, min_steps: isize, max_steps: isize) -> u32 {
+        let (width, height) = (self.map[0].len(), self.map.len());
+        let goal = Vector2D::new(width as isize - 1, height as isize - 1);
+
+        let mut queue: MinHeap<State> = MinHeap::new();
+        queue.push(State {
+            heat_loss: 0,
+            distance: 0,
+            position: Vector2D::new(0, 0),
+            direction: Vector2D::new(1, 0),
+        });
+        queue.push(State {
+            heat_loss: 0,
+            distance: 0,
+            position: Vector2D::new(0, 0),
+            direction: Vector2D::new(0, 1),
+        });
+
+        let mut seen: HashSet<(Vector2D<isize>, Vector2D<isize>)> = HashSet::new();
+        while let Some(s) = queue.pop() {
+            if s.position == goal {
+                return s.heat_loss;
+            }
+
+            if seen.contains(&(s.position, s.direction)) {
+                continue;
+            }
+            seen.insert((s.position, s.direction));
+
+            for steps in min_steps..=max_steps {
+                for d in [left(&s.direction), right(&s.direction)] {
+                    if !in_range(&self.map, &(s.position + d * steps)) {
+                        continue;
+                    }
+
+                    queue.push(s.step(&self.map, d, steps));
+                }
+            }
+        }
+
+        unreachable!()
+    }
+}
+
+impl Solution<Output1, Output2> for Day17 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        Self {
+            map: file_to_string(pathname)
+                .lines()
+                .map(|l| l.chars().map(|c| c.to_digit(10).unwrap()).collect())
+                .collect(),
+        }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.astar(1, 3)
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        self.astar(4, 10)
+    }
+}
+
+fn main() -> Result<()> {
+    Day17::main()
+}
+
+test_sample!(day_17, Day17, 102, 94);
+
+#[cfg(test)]
+mod day_17_extended {
+    use super::*;
+
+    #[test]
+    fn test_left_rotate() {
+        assert_eq!(left(&Vector2D::new(1, 0)), Vector2D::new(0, -1));
+        assert_eq!(left(&Vector2D::new(0, -1)), Vector2D::new(-1, 0));
+        assert_eq!(left(&Vector2D::new(-1, 0)), Vector2D::new(0, 1));
+        assert_eq!(left(&Vector2D::new(0, 1)), Vector2D::new(1, 0));
+    }
+
+    #[test]
+    fn test_right_rotate() {
+        assert_eq!(right(&Vector2D::new(1, 0)), Vector2D::new(0, 1));
+        assert_eq!(right(&Vector2D::new(0, -1)), Vector2D::new(1, 0));
+        assert_eq!(right(&Vector2D::new(-1, 0)), Vector2D::new(0, -1));
+        assert_eq!(right(&Vector2D::new(0, 1)), Vector2D::new(-1, 0));
+    }
+}