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CadiacCadiac
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Day 20 solutions
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‎README.md‎

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@@ -105,3 +105,4 @@ This should start the server at `localhost:8080`.
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❄️ [Day 17](aoc-solver/src/y2024/day17.rs)
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❄️ [Day 18](aoc-solver/src/y2024/day18.rs)
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❄️ [Day 19](aoc-solver/src/y2024/day19.rs)
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❄️ [Day 20](aoc-solver/src/y2024/day20.rs)

‎aoc-solver/src/y2024/day20.rs‎

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use std::collections::{HashMap, HashSet};
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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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const DIRECTIONS: [(isize, isize); 4] = [(0, -1), (1, 0), (0, 1), (-1, 0)];
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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 is_outside_bounds(height: isize, width: isize, x: isize, y: isize) -> bool {
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x < 0 || y < 0 || x >= width || y >= height
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}
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fn race_to_end(grid: &Grid, start: Coords, end: Coords) -> (Vec<Coords>, HashMap<Coords, u32>) {
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let mut distances: HashMap<Coords, u32> = HashMap::new();
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let mut route: Vec<Coords> = vec![];
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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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let mut distance = 0;
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let mut position = start;
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loop {
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route.push(position);
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distances.insert(position, distance);
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if position == end {
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return (route, distances);
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}
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for (dx, dy) in DIRECTIONS {
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let (x, y) = (position.0 as isize + dx, position.1 as isize + dy);
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if is_outside_bounds(height, width, x, y) {
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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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if grid[y as usize][x as usize] && !distances.contains_key(&next_pos) {
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position = next_pos;
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distance += 1;
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break;
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}
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}
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}
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}
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fn manhattan(a: &Coords, b: &Coords) -> u32 {
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(a.0.abs_diff(b.0) + a.1.abs_diff(b.1)) as u32
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}
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fn cheat_targets(grid: &Grid, start: &Coords, cheat_duration: u32) -> HashSet<Coords> {
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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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let mut targets = HashSet::new();
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let duration = cheat_duration as isize;
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for dy in -duration..=duration {
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let max_x = duration - dy.abs();
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for dx in -max_x..=max_x {
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let (x, y) = (start.0 as isize + dx, start.1 as isize + dy);
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if !is_outside_bounds(height, width, x, y) && grid[y as usize][x as usize] {
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targets.insert((x as usize, y as usize));
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}
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}
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}
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targets
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}
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fn explore_cheats(
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grid: &Grid,
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start: Coords,
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end: Coords,
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cheat_duration: u32,
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) -> HashMap<u32, u32> {
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let (route, distances) = race_to_end(grid, start, end);
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let fair_distance = distances[&end];
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let mut cheats: HashMap<u32, u32> = HashMap::new();
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for (distance, position) in route.iter().enumerate() {
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for cheat_target in cheat_targets(grid, position, cheat_duration).iter() {
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let remaining_distance = fair_distance - distances[cheat_target];
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let cheat_distance =
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distance as u32 + manhattan(position, cheat_target) + remaining_distance;
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let savings = fair_distance.saturating_sub(cheat_distance);
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*cheats.entry(savings).or_default() += 1;
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}
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}
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cheats
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}
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fn filter_threshold(cheats: HashMap<u32, u32>, threshold: u32) -> u32 {
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cheats
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.into_iter()
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.filter(|(distance, _cheats)| *distance >= threshold)
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.map(|(_distance, cheats)| cheats)
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.sum()
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}
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pub struct Day20;
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impl Solution for Day20 {
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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/day20.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 cheats = explore_cheats(&grid, start, end, 2);
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let good_cheats = filter_threshold(cheats, 100);
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Ok(good_cheats)
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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 cheats = explore_cheats(&grid, start, end, 20);
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let good_cheats = filter_threshold(cheats, 100);
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Ok(good_cheats)
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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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#[rustfmt::skip]
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const INPUT: &str =
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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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#######.#.#.###\n\
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#######.#.#...#\n\
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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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###############";
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#[test]
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fn it_solves_part1_example() {
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let (grid, start, end) = parse(INPUT).unwrap();
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let cheats = explore_cheats(&grid, start, end, 2);
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assert_eq!(cheats[&2], 14);
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assert_eq!(cheats[&4], 14);
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assert_eq!(cheats[&6], 2);
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assert_eq!(cheats[&8], 4);
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assert_eq!(cheats[&10], 2);
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assert_eq!(cheats[&12], 3);
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assert_eq!(cheats[&20], 1);
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assert_eq!(cheats[&36], 1);
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assert_eq!(cheats[&38], 1);
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assert_eq!(cheats[&40], 1);
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assert_eq!(cheats[&64], 1);
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}
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#[test]
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fn it_solves_part2_example() {
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let (grid, start, end) = parse(INPUT).unwrap();
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let cheats = explore_cheats(&grid, start, end, 20);
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assert_eq!(cheats[&50], 32);
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assert_eq!(cheats[&52], 31);
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assert_eq!(cheats[&56], 39);
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assert_eq!(cheats[&58], 25);
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assert_eq!(cheats[&60], 23);
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assert_eq!(cheats[&62], 20);
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assert_eq!(cheats[&64], 19);
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assert_eq!(cheats[&66], 12);
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assert_eq!(cheats[&68], 14);
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assert_eq!(cheats[&70], 12);
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assert_eq!(cheats[&72], 22);
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assert_eq!(cheats[&74], 4);
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assert_eq!(cheats[&76], 3);
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}
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#[test]
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fn it_finds_expected_cheats_1() {
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let (grid, _start, _end) = parse(INPUT).unwrap();
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assert_eq!(
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cheat_targets(&grid, &(2, 3), 1),
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HashSet::from([(1, 3), (3, 3)])
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);
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}
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#[test]
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fn it_finds_expected_cheats_2() {
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let (grid, _start, _end) = parse(INPUT).unwrap();
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assert_eq!(
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cheat_targets(&grid, &(2, 3), 2),
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HashSet::from([(1, 2), (2, 1), (3, 2), (4, 3), (1, 3), (3, 3)])
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);
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}
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#[test]
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fn it_finds_expected_cheats_3() {
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let (grid, _start, _end) = parse(INPUT).unwrap();
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assert_eq!(
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cheat_targets(&grid, &(2, 3), 3),
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HashSet::from([
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(3, 3),
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(3, 2),
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(3, 1),
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(1, 1),
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(2, 1),
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(4, 3),
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(1, 2),
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(1, 3),
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(5, 3)
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])
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);
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}
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#[test]
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fn it_finds_expected_cheats_5() {
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let (grid, _start, _end) = parse(INPUT).unwrap();
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assert_eq!(cheat_targets(&grid, &(2, 3), 5).len(), 13);
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}
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#[test]
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fn it_finds_expected_cheats_20() {
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let (grid, _start, _end) = parse(INPUT).unwrap();
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assert_eq!(cheat_targets(&grid, &(2, 3), 20).len(), 85);
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}
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}

‎aoc-solver/src/y2024/mod.rs‎

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@@ -19,14 +19,14 @@ pub mod day16;
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pub mod day17;
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pub mod day18;
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pub mod day19;
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// pub mod day20;
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pub mod day20;
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// pub mod day21;
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// pub mod day22;
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// pub mod day23;
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// pub mod day24;
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// pub mod day25;
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pub const MAX_DAYS: u8 = 19;
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pub const MAX_DAYS: u8 = 20;
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pub struct Y2024;
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@@ -52,7 +52,7 @@ impl Solver for Y2024 {
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17 => day17::Day17.run(input, 17, 2024),
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18 => day18::Day18.run(input, 18, 2024),
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19 => day19::Day19.run(input, 19, 2024),
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// 20 => day20::Day20.run(input, 20, 2024),
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20 => day20::Day20.run(input, 20, 2024),
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// 21 => day21::Day21.run(input, 21, 2024),
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// 22 => day22::Day22.run(input, 22, 2024),
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// 23 => day23::Day23.run(input, 23, 2024),
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17 => include_str!("./day17.rs"),
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18 => include_str!("./day18.rs"),
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19 => include_str!("./day19.rs"),
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// 20 => include_str!("./day20.rs"),
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20 => include_str!("./day20.rs"),
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// 21 => include_str!("./day21.rs"),
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// 22 => include_str!("./day22.rs"),
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// 23 => include_str!("./day23.rs"),

‎aoc-web/src/header.rs‎

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@@ -40,6 +40,7 @@ pub fn header(props: &HeaderProps) -> Html {
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<NavLink route={Route::Solution { year: 2024, day: 17 }} current={props.route.clone()} text={"17"}/>
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<NavLink route={Route::Solution { year: 2024, day: 18 }} current={props.route.clone()} text={"18"}/>
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<NavLink route={Route::Solution { year: 2024, day: 19 }} current={props.route.clone()} text={"19"}/>
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<NavLink route={Route::Solution { year: 2024, day: 20 }} current={props.route.clone()} text={"20"}/>
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</>
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}
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},

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