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Day 16 solutions
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‎README.md

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@@ -101,3 +101,4 @@ This should start the server at `localhost:8080`.
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❄️ [Day 13](aoc-solver/src/y2024/day13.rs)
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❄️ [Day 14](aoc-solver/src/y2024/day14.rs)
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❄️ [Day 15](aoc-solver/src/y2024/day15.rs)
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❄️ [Day 16](aoc-solver/src/y2024/day16.rs)

‎aoc-solver/src/y2024/day16.rs

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use std::{
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cmp::Ordering,
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collections::{BinaryHeap, HashMap, HashSet},
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};
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use crate::solution::{AocError, Solution};
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type Coords = (usize, usize);
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type Grid = Vec<Vec<bool>>;
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#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
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enum Direction {
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North,
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East,
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South,
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West,
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}
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impl Direction {
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fn as_delta(&self) -> (isize, isize) {
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match self {
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Direction::North => (0, -1),
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Direction::East => (1, 0),
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Direction::South => (0, 1),
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Direction::West => (-1, 0),
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}
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}
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fn rotate_left(&self) -> Direction {
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match self {
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Direction::North => Direction::West,
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Direction::East => Direction::North,
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Direction::South => Direction::East,
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Direction::West => Direction::South,
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}
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}
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fn rotate_right(&self) -> Direction {
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match self {
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Direction::North => Direction::East,
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Direction::East => Direction::South,
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Direction::South => Direction::West,
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Direction::West => Direction::North,
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}
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}
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}
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#[derive(Clone, Eq, PartialEq)]
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struct Search {
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score: u32,
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position: Coords,
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direction: Direction,
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visited: HashSet<Coords>,
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}
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impl Ord for Search {
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fn cmp(&self, other: &Self) -> Ordering {
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other.score.cmp(&self.score)
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}
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}
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impl PartialOrd for Search {
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fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
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Some(self.cmp(other))
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}
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}
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fn parse(input: &str) -> Result<(Grid, Coords, Coords), AocError> {
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let mut grid = vec![];
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let mut start = None;
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let mut end = None;
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for (y, line) in input.trim().lines().enumerate() {
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let mut row = vec![];
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for (x, tile) in line.chars().enumerate() {
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match tile {
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'#' => row.push(false),
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'.' => row.push(true),
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'S' => {
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row.push(true);
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start = Some((x, y))
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}
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'E' => {
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row.push(true);
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end = Some((x, y))
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}
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other => return Err(AocError::parse(other, "Unexpected tile")),
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}
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}
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grid.push(row);
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}
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match (start, end) {
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(Some(start), Some(end)) => Ok((grid, start, end)),
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_ => Err(AocError::parse(input, "Missing start or end")),
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}
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}
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fn dijkstra(grid: &Grid, start: Coords, end: Coords, find_all: bool) -> Option<u32> {
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let mut scores: HashMap<(Coords, Direction), u32> = HashMap::new();
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let mut heap: BinaryHeap<Search> = BinaryHeap::new();
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let height = grid.len() as isize;
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let width = grid[0].len() as isize;
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heap.push(Search {
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score: 0,
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direction: Direction::East,
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position: start,
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visited: HashSet::new(),
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});
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let mut best_score: Option<u32> = None;
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let mut best_path_tiles: HashSet<Coords> = HashSet::new();
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while let Some(Search {
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score,
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direction,
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position,
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mut visited,
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}) = heap.pop()
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{
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if !visited.insert(position) {
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continue;
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}
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if score > *scores.get(&(position, direction)).unwrap_or(&u32::MAX) {
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continue;
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}
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if position == end {
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if find_all {
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match best_score {
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None => {
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best_score = Some(score);
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best_path_tiles.extend(visited.iter());
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}
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Some(best) if best == score => {
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best_path_tiles.extend(visited.iter());
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}
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_ => {}
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}
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} else {
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return Some(score);
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}
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}
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for (next_direction, turn_cost) in [
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(direction, 0),
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(direction.rotate_left(), 1000),
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(direction.rotate_right(), 1000),
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] {
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let next_score = score + turn_cost + 1;
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let (dx, dy) = next_direction.as_delta();
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let (x, y) = (position.0 as isize + dx, position.1 as isize + dy);
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if x < 0 || y < 0 || x >= width || y >= height {
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continue;
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}
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if !grid[y as usize][x as usize] {
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continue;
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}
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let next_pos = (x as usize, y as usize);
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let best_known = scores.entry((next_pos, next_direction)).or_insert(u32::MAX);
168+
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if next_score <= *best_known {
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*best_known = next_score;
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heap.push(Search {
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score: next_score,
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direction: next_direction,
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position: next_pos,
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visited: visited.clone(),
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});
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}
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}
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}
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if find_all {
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return Some(best_path_tiles.len() as u32);
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}
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None
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}
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pub struct Day16;
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impl Solution for Day16 {
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type A = u32;
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type B = u32;
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fn default_input(&self) -> &'static str {
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include_str!("../../../inputs/2024/day16.txt")
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}
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fn part_1(&self, input: &str) -> Result<u32, AocError> {
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let (grid, start, end) = parse(input)?;
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let smallest_score =
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dijkstra(&grid, start, end, false).ok_or_else(|| AocError::logic("No path found"))?;
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Ok(smallest_score)
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}
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fn part_2(&self, input: &str) -> Result<u32, AocError> {
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let (grid, start, end) = parse(input)?;
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let smallest_score =
211+
dijkstra(&grid, start, end, true).ok_or_else(|| AocError::logic("No path found"))?;
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Ok(smallest_score)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn it_solves_part1_example_1() {
223+
assert_eq!(
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Day16.part_1(
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"###############\n\
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#.......#....E#\n\
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#.#.###.#.###.#\n\
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#.....#.#...#.#\n\
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#.###.#####.#.#\n\
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#.#.#.......#.#\n\
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#.#.#####.###.#\n\
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#...........#.#\n\
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###.#.#####.#.#\n\
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#...#.....#.#.#\n\
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#.#.#.###.#.#.#\n\
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#.....#...#.#.#\n\
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#.###.#.#.#.#.#\n\
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#S..#.....#...#\n\
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###############"
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),
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Ok(7036)
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);
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}
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#[test]
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fn it_solves_part1_example_2() {
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assert_eq!(
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Day16.part_1(
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"#################\n\
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#...#...#...#..E#\n\
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#.#.#.#.#.#.#.#.#\n\
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#.#.#.#...#...#.#\n\
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#.#.#.#.###.#.#.#\n\
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#...#.#.#.....#.#\n\
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#.#.#.#.#.#####.#\n\
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#.#...#.#.#.....#\n\
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#.#.#####.#.###.#\n\
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#.#.#.......#...#\n\
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#.#.###.#####.###\n\
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#.#.#...#.....#.#\n\
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#.#.#.#####.###.#\n\
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#.#.#.........#.#\n\
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#.#.#.#########.#\n\
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#S#.............#\n\
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#################"
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),
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Ok(11048)
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);
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}
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#[test]
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fn it_solves_part2_example_1() {
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assert_eq!(
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Day16.part_2(
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"###############\n\
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#.......#....E#\n\
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#.#.###.#.###.#\n\
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#.....#.#...#.#\n\
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#.###.#####.#.#\n\
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#.#.#.......#.#\n\
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#.#.#####.###.#\n\
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#...........#.#\n\
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###.#.#####.#.#\n\
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#...#.....#.#.#\n\
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#.#.#.###.#.#.#\n\
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#.....#...#.#.#\n\
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#.###.#.#.#.#.#\n\
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#S..#.....#...#\n\
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###############"
290+
),
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Ok(45)
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);
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}
294+
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#[test]
296+
fn it_solves_part2_example_2() {
297+
assert_eq!(
298+
Day16.part_2(
299+
"#################\n\
300+
#...#...#...#..E#\n\
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#.#.#.#.#.#.#.#.#\n\
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#.#.#.#...#...#.#\n\
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#.#.#.#.###.#.#.#\n\
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#...#.#.#.....#.#\n\
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#.#.#.#.#.#####.#\n\
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#.#...#.#.#.....#\n\
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#.#.#####.#.###.#\n\
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#.#.#.......#...#\n\
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#.#.###.#####.###\n\
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#.#.#...#.....#.#\n\
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#.#.#.#####.###.#\n\
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#.#.#.........#.#\n\
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#.#.#.#########.#\n\
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#S#.............#\n\
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#################"
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),
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Ok(64)
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);
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}
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}

‎aoc-solver/src/y2024/mod.rs

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Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@ pub mod day12;
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pub mod day13;
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pub mod day14;
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pub mod day15;
18-
// pub mod day16;
18+
pub mod day16;
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// pub mod day17;
2020
// pub mod day18;
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// pub mod day19;
@@ -26,7 +26,7 @@ pub mod day15;
2626
// pub mod day24;
2727
// pub mod day25;
2828

29-
pub const MAX_DAYS: u8 = 15;
29+
pub const MAX_DAYS: u8 = 16;
3030

3131
pub struct Y2024;
3232

@@ -48,7 +48,7 @@ impl Solver for Y2024 {
4848
13 => day13::Day13.run(input, 13, 2024),
4949
14 => day14::Day14.run(input, 14, 2024),
5050
15 => day15::Day15.run(input, 15, 2024),
51-
// 16 => day16::Day16.run(input, 16, 2024),
51+
16 => day16::Day16.run(input, 16, 2024),
5252
// 17 => day17::Day17.run(input, 17, 2024),
5353
// 18 => day18::Day18.run(input, 18, 2024),
5454
// 19 => day19::Day19.run(input, 19, 2024),
@@ -90,7 +90,7 @@ impl Solver for Y2024 {
9090
13 => include_str!("./day13.rs"),
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14 => include_str!("./day14.rs"),
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15 => include_str!("./day15.rs"),
93-
// 16 => include_str!("./day16.rs"),
93+
16 => include_str!("./day16.rs"),
9494
// 17 => include_str!("./day17.rs"),
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// 18 => include_str!("./day18.rs"),
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// 19 => include_str!("./day19.rs"),

‎aoc-web/src/header.rs

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@@ -36,6 +36,7 @@ pub fn header(props: &HeaderProps) -> Html {
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<NavLink route={Route::EasterEgg} current={props.route.clone()} text={"14+"}/>
3737
<NavLink route={Route::Solution { year: 2024, day: 15 }} current={props.route.clone()} text={"15"}/>
3838
<NavLink route={Route::WarehouseRobot} current={props.route.clone()} text={"15+"}/>
39+
<NavLink route={Route::Solution { year: 2024, day: 15 }} current={props.route.clone()} text={"16"}/>
3940
</>
4041
}
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},

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