From f72e98c58697e4886f5c58d2689bacd044e49fd7 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Mon, 3 Jul 2023 10:57:50 +0200
Subject: [PATCH] day(24): add solution

Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 samples/day24.txt |   6 ++
 src/bin/day24.rs  | 144 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 150 insertions(+)
 create mode 100644 samples/day24.txt
 create mode 100644 src/bin/day24.rs

diff --git a/samples/day24.txt b/samples/day24.txt
new file mode 100644
index 0000000..6b9b892
--- /dev/null
+++ b/samples/day24.txt
@@ -0,0 +1,6 @@
+#.######
+#>>.<^<#
+#.<..<<#
+#>v.><>#
+#<^v^^>#
+######.#
\ No newline at end of file
diff --git a/src/bin/day24.rs b/src/bin/day24.rs
new file mode 100644
index 0000000..aaa0ef9
--- /dev/null
+++ b/src/bin/day24.rs
@@ -0,0 +1,144 @@
+use std::{collections::HashSet, ops::Index};
+
+use aoc_2022::*;
+
+type Input = Basin;
+type Output = isize;
+
+type Position = Vector3D<isize>;
+
+struct Basin {
+    map: Vec<Vec<char>>,
+    rows: isize,
+    cols: isize,
+    entry: Position,
+    exit: Position,
+}
+
+impl Index<Position> for Basin {
+    type Output = char;
+
+    fn index(&self, index: Position) -> &Self::Output {
+        if index.y() == 0 && index.x() == 1 {
+            // entry
+            return &'.';
+        }
+
+        if index.y() == self.rows - 1 && index.x() == self.cols - 2 {
+            // exit
+            return &'.';
+        }
+
+        if index.y() <= 0
+            || index.y() >= self.rows - 1
+            || index.x() <= 0
+            || index.x() >= self.cols - 1
+        {
+            // out of bounds
+            return &'#';
+        }
+
+        // We need to account for the loops of the blizzards
+        let x_mod = self.cols - 2;
+        let y_mod = self.rows - 2;
+
+        let x_w = ((index.x() - 1 + x_mod - (index.z() % x_mod)) % x_mod + 1) as usize;
+        let x_e = ((index.x() - 1 + x_mod + (index.z() % x_mod)) % x_mod + 1) as usize;
+        let y_n = ((index.y() - 1 + y_mod - (index.z() % y_mod)) % y_mod + 1) as usize;
+        let y_s = ((index.y() - 1 + y_mod + (index.z() % y_mod)) % y_mod + 1) as usize;
+
+        if self.map[index.y() as usize][x_w] == '>' {
+            return &self.map[index.y() as usize][x_w];
+        }
+
+        if self.map[index.y() as usize][x_e] == '<' {
+            return &self.map[index.y() as usize][x_e];
+        }
+
+        if self.map[y_n][index.x() as usize] == 'v' {
+            return &self.map[y_n][index.x() as usize];
+        }
+
+        if self.map[y_s][index.x() as usize] == '^' {
+            return &self.map[y_s][index.x() as usize];
+        }
+
+        &'.'
+    }
+}
+
+fn find_exit(basin: &Input, entry: Position, exit: Position) -> Position {
+    let next_positions = |p| {
+        [(0, 0, 1), (0, -1, 1), (0, 1, 1), (-1, 0, 1), (1, 0, 1)]
+            .iter()
+            .filter_map(move |&(x, y, t)| {
+                let next_p = p + Vector3D::new(x, y, t);
+
+                if basin[next_p] == '.' {
+                    Some(next_p)
+                } else {
+                    None
+                }
+            })
+    };
+
+    let cost = |p: Position| p.z() as usize + exit.y().abs_diff(p.y()) + exit.x().abs_diff(p.x());
+
+    let mut seen: HashSet<Position> = HashSet::new();
+    let mut q: MinHeap<(usize, Position)> = MinHeap::new();
+    q.push((cost(entry), entry));
+
+    while let Some((_, pos)) = q.pop() {
+        // debug!("Dequeued: {:?}", pos);
+        if pos.y() == exit.y() && pos.x() == exit.x() {
+            return pos;
+        }
+
+        for next_pos in next_positions(pos) {
+            if !seen.contains(&next_pos) {
+                seen.insert(next_pos);
+                q.push((cost(next_pos), next_pos));
+            }
+        }
+    }
+
+    unreachable!()
+}
+
+struct Day24;
+impl Solution<Input, Output> for Day24 {
+    fn parse_input<P: AsRef<Path>>(pathname: P) -> Input {
+        let map: Vec<Vec<char>> = file_to_string(pathname)
+            .lines()
+            .map(|l| l.chars().collect())
+            .collect();
+        let (rows, cols) = (map.len() as isize, map[0].len() as isize);
+
+        Basin {
+            map,
+            rows,
+            cols,
+            entry: Vector3D::new(1, 0, 0),
+            exit: Vector3D::new(cols - 2, rows - 1, isize::MAX),
+        }
+    }
+
+    fn part_1(input: &Input) -> Output {
+        find_exit(input, input.entry, input.exit).z()
+    }
+
+    fn part_2(input: &Input) -> Output {
+        let to_exit = find_exit(input, input.entry, input.exit);
+        let to_entry = find_exit(input, to_exit, input.entry);
+        let back_to_exit = find_exit(input, to_entry, input.exit);
+
+        back_to_exit.z()
+    }
+}
+
+fn main() -> Result<()> {
+    // Day24::run("sample")
+    Day24::main()
+}
+
+test_sample!(day_24, Day24, 18, 54);