Add day18

day18/Cargo.lock

@@ -0,0 +1,16 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day18"
+version = "0.1.0"
+dependencies = [
+ "glam",
+]
+
+[[package]]
+name = "glam"
+version = "0.29.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc46dd3ec48fdd8e693a98d2b8bafae273a2d54c1de02a2a7e3d57d501f39677"

day18/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day18"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+glam = "0.29.2"

day18/src/main.rs

@@ -0,0 +1,149 @@
+use std::{cmp::Reverse, collections::BinaryHeap};
+
+use glam::IVec2;
+
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+use Direction::*;
+
+impl Direction {
+    fn to_vec(&self) -> IVec2 {
+        match self {
+            Up => IVec2::new(-1, 0),
+            Down => IVec2::new(1, 0),
+            Left => IVec2::new(0, -1),
+            Right => IVec2::new(0, 1),
+        }
+    }
+    fn all() -> Vec<Self> {
+        vec![Up, Down, Left, Right]
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+enum Tile {
+    Corrupted,
+    Safe,
+}
+use Tile::*;
+
+fn parse(input: &str) -> Vec<IVec2> {
+    input
+        .lines()
+        .map(|l| {
+            let (y, x) = l.split_once(',').unwrap();
+            IVec2 {
+                x: x.parse().unwrap(),
+                y: y.parse().unwrap(),
+            }
+        })
+        .collect()
+}
+
+fn build_grid(dimensions: &IVec2, bytes_amount: usize, positions: &[IVec2]) -> Vec<Vec<Tile>> {
+    let mut grid = vec![];
+    for px in 0..=dimensions.x {
+        let mut line = vec![];
+        for py in 0..=dimensions.y {
+            if positions[..bytes_amount].contains(&IVec2::new(px, py)) {
+                line.push(Corrupted);
+            } else {
+                line.push(Safe);
+            }
+        }
+        grid.push(line);
+    }
+    grid
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+struct Node {
+    score: u32,
+    position: IVec2,
+}
+
+impl Ord for Node {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.score.cmp(&other.score)
+    }
+}
+
+impl PartialOrd for Node {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn find_path(grid: &[Vec<Tile>], start_pos: &IVec2, end_pos: &IVec2) -> u32 {
+    let mut distances = vec![vec![u32::MAX; grid[0].len()]; grid.len()];
+    let mut to_visit = BinaryHeap::new();
+
+    distances[start_pos.x as usize][start_pos.y as usize] = 0;
+    to_visit.push(Reverse(Node {
+        score: 0,
+        position: *start_pos,
+    }));
+
+    while let Some(Reverse(curr)) = to_visit.pop() {
+        if curr.position == *end_pos {
+            return curr.score;
+        }
+
+        if curr.score > distances[curr.position.x as usize][curr.position.y as usize] {
+            continue;
+        }
+
+        for direction in Direction::all() {
+            let new_pos = curr.position + direction.to_vec();
+            let Some(Some(t)) = grid
+                .get(new_pos.x as usize)
+                .map(|l| l.get(new_pos.y as usize))
+            else {
+                continue;
+            };
+            if *t != Corrupted {
+                let new_score = curr.score + 1;
+                if new_score < distances[new_pos.x as usize][new_pos.y as usize] {
+                    distances[new_pos.x as usize][new_pos.y as usize] = new_score;
+                    to_visit.push(Reverse(Node {
+                        score: new_score,
+                        position: new_pos,
+                    }));
+                }
+            }
+        }
+    }
+
+    u32::MAX
+}
+
+fn part1(positions: &[IVec2], dimensions: &IVec2) -> u32 {
+    let grid = build_grid(dimensions, 1024, positions);
+    find_path(&grid, &IVec2::new(0, 0), dimensions)
+}
+
+fn part2(positions: &[IVec2], dimensions: &IVec2) -> String {
+    let start_pos = IVec2::new(0, 0);
+    // todo: use binary search
+    for i in 1024.. {
+        let grid = build_grid(dimensions, i, positions);
+        if find_path(&grid, &start_pos, dimensions) == u32::MAX {
+            return positions
+                .get(i - 1)
+                .map(|p| format!("{},{}", p.y, p.x))
+                .unwrap();
+        }
+    }
+    unreachable!()
+}
+
+fn main() {
+    let input = parse(include_str!("../input.txt"));
+    let size = IVec2::new(70, 70);
+    println!("{}", part1(&input, &size));
+    println!("{}", part2(&input, &size));
+}