Day 18 solutions using A-star bruteforce

Author: Cadiac

README.md

@@ -103,3 +103,4 @@ This should start the server at `localhost:8080`.
 ❄️ [Day 15](aoc-solver/src/y2024/day15.rs)
 ❄️ [Day 16](aoc-solver/src/y2024/day16.rs)
 ❄️ [Day 17](aoc-solver/src/y2024/day17.rs)
+❄️ [Day 18](aoc-solver/src/y2024/day18.rs)

aoc-solver/src/y2024/day18.rs

@@ -0,0 +1,203 @@
+use std::{
+    cmp::Ordering,
+    collections::{BinaryHeap, HashMap, HashSet},
+};
+
+use itertools::Itertools;
+
+use crate::solution::{AocError, Solution};
+
+type Coords = (usize, usize);
+
+const DIRECTIONS: [(isize, isize); 4] = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+#[derive(Clone, Eq, PartialEq)]
+struct Search {
+    steps: u32,
+    position: Coords,
+}
+
+impl Ord for Search {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.steps.cmp(&self.steps)
+    }
+}
+
+impl PartialOrd for Search {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn parse(input: &str) -> Result<Vec<Coords>, AocError> {
+    let bytes = input
+        .lines()
+        .map(|line| {
+            line.split_once(",")
+                .and_then(|(x, y)| {
+                    let pos = (x.parse::<usize>().ok()?, y.parse::<usize>().ok()?);
+
+                    Some(pos)
+                })
+                .ok_or_else(|| AocError::parse(input, "Invalid input"))
+        })
+        .try_collect()?;
+
+    Ok(bytes)
+}
+
+// Manhattan distance as the heuristic function
+fn heuristic(a: Coords, b: Coords) -> u32 {
+    (a.0.abs_diff(b.0) + a.1.abs_diff(b.1)) as u32
+}
+
+pub fn a_star(corrupted: &[Coords], start: Coords, end: Coords) -> Option<u32> {
+    let corrupted: HashSet<&Coords> = corrupted.iter().collect();
+    let width = end.0 as isize + 1;
+    let height = end.1 as isize + 1;
+
+    if corrupted.contains(&start) || corrupted.contains(&end) {
+        return None;
+    }
+
+    let mut g = HashMap::new();
+    let mut f = HashMap::new();
+    let mut open_set = BinaryHeap::new();
+    let mut closed_set = HashSet::new();
+
+    g.insert(start, 0);
+    f.insert(start, heuristic(start, end));
+
+    open_set.push(Search {
+        steps: f[&start],
+        position: start,
+    });
+
+    while let Some(Search { position, .. }) = open_set.pop() {
+        if position == end {
+            return g.get(&position).cloned();
+        }
+
+        if closed_set.contains(&position) {
+            continue;
+        }
+
+        closed_set.insert(position);
+
+        for (dx, dy) in DIRECTIONS {
+            let (x, y) = (position.0 as isize + dx, position.1 as isize + dy);
+            if x < 0 || y < 0 || x >= width || y >= height {
+                continue;
+            }
+
+            let neighbour = (x as usize, y as usize);
+
+            if corrupted.contains(&neighbour) || closed_set.contains(&neighbour) {
+                continue;
+            }
+
+            let tentative_g = g.entry(position).or_default().saturating_add(1);
+            let existing_g = g.get(&neighbour).unwrap_or(&u32::MAX);
+
+            if tentative_g < *existing_g {
+                g.insert(neighbour, tentative_g);
+                f.insert(neighbour, tentative_g + heuristic(neighbour, end));
+
+                open_set.push(Search {
+                    steps: tentative_g + heuristic(neighbour, end),
+                    position: neighbour,
+                });
+            }
+        }
+    }
+
+    None
+}
+
+pub struct Day18;
+impl Solution for Day18 {
+    type A = u32;
+    type B = String;
+
+    fn default_input(&self) -> &'static str {
+        include_str!("../../../inputs/2024/day18.txt")
+    }
+
+    fn part_1(&self, input: &str) -> Result<u32, AocError> {
+        let corrupted = parse(input)?;
+
+        let start = (0, 0);
+        let end = (70, 70);
+        let min_distance = a_star(&corrupted[0..1024], start, end)
+            .ok_or_else(|| AocError::logic("No path found"))?;
+
+        Ok(min_distance)
+    }
+
+    fn part_2(&self, input: &str) -> Result<String, AocError> {
+        let corrupted = parse(input)?;
+
+        let mut t = 1024;
+        let start = (0, 0);
+        let end = (70, 70);
+
+        while a_star(&corrupted[0..t], start, end).is_some() {
+            t += 1;
+        }
+
+        Ok(format!("{},{}", corrupted[t - 1].0, corrupted[t - 1].1))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "5,4\n\
+        4,2\n\
+        4,5\n\
+        3,0\n\
+        2,1\n\
+        6,3\n\
+        2,4\n\
+        1,5\n\
+        0,6\n\
+        3,3\n\
+        2,6\n\
+        5,1\n\
+        1,2\n\
+        5,5\n\
+        2,5\n\
+        6,5\n\
+        1,4\n\
+        0,4\n\
+        6,4\n\
+        1,1\n\
+        6,1\n\
+        1,0\n\
+        0,5\n\
+        1,6\n\
+        2,0";
+
+    #[test]
+    fn it_solves_part1_example() {
+        let bytes = parse(TEST_INPUT).unwrap();
+
+        let min_distance = a_star(&bytes[0..12], (0, 0), (6, 6));
+
+        assert_eq!(min_distance, Some(22));
+    }
+
+    #[test]
+    fn it_solves_part2_example() {
+        let bytes = parse(TEST_INPUT).unwrap();
+
+        let mut t = 12;
+
+        while a_star(&bytes[0..t], (0, 0), (6, 6)).is_some() {
+            t += 1;
+        }
+
+        assert_eq!(t, 21);
+    }
+}

aoc-solver/src/y2024/mod.rs

@@ -17,7 +17,7 @@ pub mod day14;
 pub mod day15;
 pub mod day16;
 pub mod day17;
-// pub mod day18;
+pub mod day18;
 // pub mod day19;
 // pub mod day20;
 // pub mod day21;
@@ -26,7 +26,7 @@ pub mod day17;
 // pub mod day24;
 // pub mod day25;
 
-pub const MAX_DAYS: u8 = 17;
+pub const MAX_DAYS: u8 = 18;
 
 pub struct Y2024;
 
@@ -50,7 +50,7 @@ impl Solver for Y2024 {
             15 => day15::Day15.run(input, 15, 2024),
             16 => day16::Day16.run(input, 16, 2024),
             17 => day17::Day17.run(input, 17, 2024),
-            // 18 => day18::Day18.run(input, 18, 2024),
+            18 => day18::Day18.run(input, 18, 2024),
             // 19 => day19::Day19.run(input, 19, 2024),
             // 20 => day20::Day20.run(input, 20, 2024),
             // 21 => day21::Day21.run(input, 21, 2024),
@@ -92,7 +92,7 @@ impl Solver for Y2024 {
             15 => include_str!("./day15.rs"),
             16 => include_str!("./day16.rs"),
             17 => include_str!("./day17.rs"),
-            // 18 => include_str!("./day18.rs"),
+            18 => include_str!("./day18.rs"),
             // 19 => include_str!("./day19.rs"),
             // 20 => include_str!("./day20.rs"),
             // 21 => include_str!("./day21.rs"),

aoc-web/src/header.rs

@@ -38,6 +38,7 @@ pub fn header(props: &HeaderProps) -> Html {
                                     <NavLink route={Route::WarehouseRobot} current={props.route.clone()} text={"15+"}/>
                                     <NavLink route={Route::Solution { year: 2024, day: 16 }} current={props.route.clone()} text={"16"}/>
                                     <NavLink route={Route::Solution { year: 2024, day: 17 }} current={props.route.clone()} text={"17"}/>
+                                    <NavLink route={Route::Solution { year: 2024, day: 18 }} current={props.route.clone()} text={"18"}/>
                                 </>
                             }
                         },