Year 2024 Day 15

Author: maneatingape

README.md

@@ -86,6 +86,7 @@ Performance is reasonable even on older hardware, for example a 2011 MacBook Pro
 | 12 | [Garden Groups](https://adventofcode.com/2024/day/12) | [Source](src/year2024/day12.rs) | 289 |
 | 13 | [Claw Contraption](https://adventofcode.com/2024/day/13) | [Source](src/year2024/day13.rs) | 14 |
 | 14 | [Restroom Redoubt](https://adventofcode.com/2024/day/14) | [Source](src/year2024/day14.rs) | 74 |
+| 15 | [Warehouse Woes](https://adventofcode.com/2024/day/15) | [Source](src/year2024/day15.rs) | 379 |
 
 ## 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
+    day14, day15
 );

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
+    day14, day15
 );

src/main.rs

@@ -140,5 +140,5 @@ run!(year2023
 
 run!(year2024
     day01, day02, day03, day04, day05, day06, day07, day08, day09, day10, day11, day12, day13,
-    day14
+    day14, day15
 );

src/year2024/day15.rs

@@ -0,0 +1,154 @@
+//! # Warehouse Woes
+use crate::util::grid::*;
+use crate::util::point::*;
+use std::mem::swap;
+
+type Input<'a> = (Grid<u8>, &'a str);
+
+pub fn parse(input: &str) -> Input<'_> {
+    let (prefix, suffix) = input.split_once("\n\n").unwrap();
+    let grid = Grid::parse(prefix);
+    (grid, suffix)
+}
+
+pub fn part1(input: &Input<'_>) -> i32 {
+    let (grid, moves) = input;
+
+    let mut grid = grid.clone();
+    let mut position = grid.find(b'@').unwrap();
+
+    for b in moves.bytes() {
+        let direction = match b {
+            b'<' => LEFT,
+            b'>' => RIGHT,
+            b'^' => UP,
+            b'v' => DOWN,
+            _ => continue,
+        };
+
+        push_one(&mut grid, &mut position, direction);
+    }
+
+    gps(&grid, b'O')
+}
+
+pub fn part2(input: &Input<'_>) -> i32 {
+    let (grid, moves) = input;
+
+    let mut grid = stretch(grid);
+    let mut position = grid.find(b'@').unwrap();
+
+    let mut todo = Vec::new();
+    let mut seen = grid.same_size_with(usize::MAX);
+
+    for (id, b) in moves.bytes().enumerate() {
+        match b {
+            b'<' => push_one(&mut grid, &mut position, LEFT),
+            b'>' => push_one(&mut grid, &mut position, RIGHT),
+            b'^' => push_two(&mut grid, &mut todo, &mut seen, id, &mut position, UP),
+            b'v' => push_two(&mut grid, &mut todo, &mut seen, id, &mut position, DOWN),
+            _ => (),
+        }
+    }
+
+    gps(&grid, b'[')
+}
+
+fn push_one(grid: &mut Grid<u8>, start: &mut Point, direction: Point) {
+    let mut position = *start;
+    let mut size = 1;
+
+    loop {
+        match grid[position] {
+            b'#' => return,
+            b'.' => break,
+            _ => {
+                position += direction;
+                size += 1;
+            }
+        }
+    }
+
+    let mut previous = b'.';
+    let mut position = *start;
+
+    for _ in 0..size {
+        swap(&mut grid[position], &mut previous);
+        position += direction;
+    }
+
+    *start += direction;
+}
+
+fn push_two(grid: &mut Grid<u8>, todo: &mut Vec<Point>, seen: &mut Grid<usize>, id: usize, start: &mut Point, direction: Point) {
+    let mut index = 0;
+
+    todo.clear();
+    todo.push(*start);
+
+    while index < todo.len() {
+        let next = todo[index] + direction;
+        index += 1;
+
+        let other = match grid[next] {
+            b'#' => return,
+            b'[' => RIGHT,
+            b']' => LEFT,
+            _ => continue,
+        };
+
+        let first = next;
+        if seen[first] != id {
+            seen[first] = id;
+            todo.push(first);
+        }
+
+        let second = next + other;
+        if seen[second] != id {
+            seen[second] = id;
+            todo.push(second);
+        }
+    }
+
+    for &point in todo.iter().rev() {
+        grid[point + direction] = grid[point];
+        grid[point] = b'.';
+    }
+
+    *start += direction;
+}
+
+fn stretch(grid: &Grid<u8>) -> Grid<u8> {
+    let mut next = Grid::new(grid.width * 2, grid.height, b'.');
+
+    for y in 0..grid.height {
+        for x in 0..grid.width {
+            let (left, right) = match grid[Point::new(x, y)] {
+                b'#' => (b'#', b'#'),
+                b'O' => (b'[', b']'),
+                b'@' => (b'@', b'.'),
+                _ => continue,
+            };
+
+            next[Point::new(2 * x, y)] = left;
+            next[Point::new(2 * x + 1, y)] = right;
+        }
+    }
+
+    next
+}
+
+fn gps(grid: &Grid<u8>, needle: u8) -> i32 {
+    let mut result = 0;
+
+    for y in 0..grid.height {
+        for x in 0..grid.width {
+            let point = Point::new(x, y);
+            if grid[point] == needle {
+                result += 100 * point.y + point.x;
+            }
+        }
+    }
+
+    result
+}

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
+    day14, day15
 );

tests/year2024/day15.rs

@@ -0,0 +1,36 @@
+use aoc::year2024::day15::*;
+
+const EXAMPLE: &str = "\
+##########
+#..O..O.O#
+#......O.#
+#.OO..O.O#
+#[email protected].#
+#O#..O...#
+#O..O..O.#
+#.OO.O.OO#
+#....O...#
+##########
+
+<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
+vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
+><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
+<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
+^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
+^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
+>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
+<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
+^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
+v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^";
+
+#[test]
+fn part1_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part1(&input), 10092);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(EXAMPLE);
+    assert_eq!(part2(&input), 9021);
+}