Year 2024 Day 18

Author: maneatingape

README.md

@@ -89,6 +89,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 15 | [Warehouse Woes](https://adventofcode.com/2024/day/15) | [Source](src/year2024/day15.rs) | 303 |
 | 16 | [Reindeer Maze](https://adventofcode.com/2024/day/16) | [Source](src/year2024/day16.rs) | 390 |
 | 17 | [Chronospatial Computer](https://adventofcode.com/2024/day/17) | [Source](src/year2024/day17.rs) | 2 |
+| 18 | [RAM Run](https://adventofcode.com/2024/day/18) | [Source](src/year2024/day18.rs) | 90 |
 
 ## 2023
 

benches/benchmark.rs

@@ -88,5 +88,5 @@ benchmark!(year2023
 
 benchmark!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16, day17
+    day14, day15, day16, day17, day18
 );

src/lib.rs

@@ -68,5 +68,5 @@ library!(year2023 "Restore global snow production."
 
 library!(year2024 "Locate the Chief Historian in time for the big Christmas sleigh launch."
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16, day17
+    day14, day15, day16, day17, day18
 );

src/main.rs

@@ -142,5 +142,5 @@ run!(year2023
 
 run!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16, day17
+    day14, day15, day16, day17, day18
 );

src/year2024/day18.rs

@@ -0,0 +1,67 @@
+use crate::util::grid::*;
+use crate::util::iter::*;
+use crate::util::parse::*;
+use crate::util::point::*;
+use std::collections::VecDeque;
+
+type Input = (Vec<(usize, Point)>, Grid<usize>);
+
+pub fn parse(input: &str) -> Input {
+    let points: Vec<_> = input
+        .iter_signed::<i32>()
+        .chunk::<2>()
+        .map(|[x, y]| Point::new(x, y))
+        .enumerate()
+        .collect();
+
+    let mut grid = Grid::new(71, 71, usize::MAX);
+    points.iter().for_each(|&(i, p)| grid[p] = i);
+
+    (points, grid)
+}
+
+pub fn part1(input: &Input) -> u32 {
+    let (_, grid) = input;
+
+    let todo = &mut VecDeque::new();
+    let seen = &mut grid.same_size_with(usize::MAX);
+
+    bfs(grid, todo, seen, 1024).unwrap()
+}
+
+pub fn part2(input: &Input) -> String {
+    let (points, grid) = input;
+
+    let todo = &mut VecDeque::new();
+    let seen = &mut grid.same_size_with(usize::MAX);
+
+    let first = points.partition_point(|&(id, _)| bfs(grid, todo, seen, id).is_some());
+    let blocker = points[first + 1].1;
+    format!("{},{}", blocker.x, blocker.y)
+}
+
+fn bfs(
+    grid: &Grid<usize>,
+    todo: &mut VecDeque<(Point, u32)>,
+    seen: &mut Grid<usize>,
+    id: usize,
+) -> Option<u32> {
+    todo.clear();
+    todo.push_back((ORIGIN, 0));
+    seen[ORIGIN] = id;
+
+    while let Some((position, cost)) = todo.pop_front() {
+        if position == Point::new(70, 70) {
+            return Some(cost);
+        }
+
+        for next in ORTHOGONAL.map(|o| position + o) {
+            if grid.contains(next) && grid[next] > id && seen[next] != id {
+                todo.push_back((next, cost + 1));
+                seen[next] = id;
+            }
+        }
+    }
+
+    None
+}

tests/test.rs

@@ -81,5 +81,5 @@ test!(year2023
 
 test!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14, day15, day16, day17
+    day14, day15, day16, day17, day18
 );

tests/year2024/day18.rs

@@ -0,0 +1,9 @@
+#[test]
+fn part1_test() {
+    // No test
+}
+
+#[test]
+fn part2_test() {
+    // No test
+}