jonas.tngl.sh
Advent of Code solutions in Rust
feat: day 4 of AoC 2025
+220
-2
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Cargo.lock
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Cargo.lock
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aoc_2025/Cargo.toml
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aoc_2025/Cargo.toml
+216
aoc_2025/src/day04.rs
+216
aoc_2025/src/day04.rs
···
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use std::collections::HashSet;
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use aoc_companion::prelude::*;
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use aoc_utils::geometry::{ParseMapError, Point};
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use aoc_utils::linalg::Vector;
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use itertools::Itertools;
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pub(crate) struct Door {
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rolls: HashSet<Vector<usize, 2>>,
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}
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impl<'input> Solution<'input> for Door {
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fn parse(input: &'input str) -> Result<Self, ParseMapError<ParseTileError>> {
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Ok(Door {
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rolls: parse_roll_locations(input)?,
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})
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}
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fn part1(&self) -> usize {
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accessible_roll_locations(&self.rolls).count()
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}
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fn part2(&self) -> usize {
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self.rolls.len() - non_removable_roll_locations(self.rolls.clone()).len()
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}
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}
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#[derive(Debug, thiserror::Error)]
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pub(crate) enum ParseTileError {
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#[error("invalid map tile: {tile:?}")]
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InvalidTile { tile: u8 },
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}
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fn parse_roll_locations(
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input: &str,
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) -> Result<HashSet<Vector<usize, 2>>, ParseMapError<ParseTileError>> {
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let map = aoc_utils::geometry::try_parse_map(input, |tile| match tile {
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b'@' => Ok(true),
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b'.' => Ok(false),
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_ => Err(ParseTileError::InvalidTile { tile }),
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})?;
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Ok(map
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.indexed_iter()
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.filter(|(_, is_roll)| **is_roll)
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.map(|((y, x), _)| Vector([x, y]))
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.collect())
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}
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fn accessible_roll_locations(
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rolls: &HashSet<Vector<usize, 2>>,
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) -> impl Iterator<Item = Vector<usize, 2>> {
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rolls
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.iter()
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.filter(|r| r.neighbors().filter(|n| rolls.contains(n)).count() < 4)
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.copied()
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}
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fn with_accessible_rolls_removed(rolls: &HashSet<Vector<usize, 2>>) -> HashSet<Vector<usize, 2>> {
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rolls
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.difference(&accessible_roll_locations(rolls).collect())
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.copied()
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.collect()
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}
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fn non_removable_roll_locations(rolls: HashSet<Vector<usize, 2>>) -> HashSet<Vector<usize, 2>> {
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std::iter::successors(Some(rolls), |prev| {
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Some(with_accessible_rolls_removed(prev))
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})
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.tuple_windows()
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.find_map(|(lhs, rhs)| (lhs == rhs).then_some(lhs))
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.unwrap()
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}
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#[cfg(test)]
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mod tests {
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use itertools::Itertools;
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use super::*;
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const EXAMPLE_INPUT: &str = "\
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..@@.@@@@.
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@@@.@.@.@@
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@@@@@.@.@@
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@.@@@@..@.
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@@.@@@@.@@
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.@@@@@@@.@
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.@.@.@.@@@
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@.@@@.@@@@
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.@@@@@@@@.
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@.@.@@@.@.";
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const EXAMPLE_ACCESSIBLE_ROLLS: &str = "\
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..@@.@@.@.
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@.........
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......@...
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..........
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@........@
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..........
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..........
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@.........
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..........
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@.@.....@.";
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const EXAMPLE_NON_REMOVABLE_ROLLS: &str = "\
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..........
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..........
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..........
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....@@....
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...@@@@...
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...@@@@@..
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...@.@.@@.
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...@@.@@@.
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...@@@@@..
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....@@@...";
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const EXAMPLE_ROLL_LOCATIONS: &[Vector<usize, 2>] = &[
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Vector([0, 1]),
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Vector([0, 2]),
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Vector([0, 3]),
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Vector([0, 4]),
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Vector([0, 7]),
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Vector([0, 9]),
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Vector([1, 1]),
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Vector([1, 2]),
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Vector([1, 4]),
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Vector([1, 5]),
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Vector([1, 6]),
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Vector([1, 8]),
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Vector([2, 0]),
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Vector([2, 1]),
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Vector([2, 2]),
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Vector([2, 3]),
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Vector([2, 5]),
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Vector([2, 7]),
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Vector([2, 8]),
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Vector([2, 9]),
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Vector([3, 0]),
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Vector([3, 2]),
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Vector([3, 3]),
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Vector([3, 4]),
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Vector([3, 5]),
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Vector([3, 6]),
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Vector([3, 7]),
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Vector([3, 8]),
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Vector([4, 1]),
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Vector([4, 2]),
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Vector([4, 3]),
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Vector([4, 4]),
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Vector([4, 5]),
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Vector([4, 7]),
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Vector([4, 8]),
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Vector([4, 9]),
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Vector([5, 0]),
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Vector([5, 3]),
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Vector([5, 4]),
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Vector([5, 5]),
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Vector([5, 6]),
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Vector([5, 8]),
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Vector([5, 9]),
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Vector([6, 0]),
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Vector([6, 1]),
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Vector([6, 2]),
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Vector([6, 4]),
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Vector([6, 5]),
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Vector([6, 7]),
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Vector([6, 8]),
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Vector([6, 9]),
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Vector([7, 0]),
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Vector([7, 5]),
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Vector([7, 6]),
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Vector([7, 7]),
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Vector([7, 8]),
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Vector([8, 0]),
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Vector([8, 1]),
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Vector([8, 2]),
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Vector([8, 3]),
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Vector([8, 4]),
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Vector([8, 6]),
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Vector([8, 7]),
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Vector([8, 8]),
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Vector([8, 9]),
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Vector([9, 1]),
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Vector([9, 2]),
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Vector([9, 4]),
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Vector([9, 5]),
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Vector([9, 6]),
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Vector([9, 7]),
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];
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#[test]
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fn parse_example_roll_locations() {
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itertools::assert_equal(
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parse_roll_locations(EXAMPLE_INPUT).unwrap().iter().sorted(),
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EXAMPLE_ROLL_LOCATIONS,
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);
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}
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#[test]
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fn accessible_rolls_in_example() {
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assert_eq!(
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HashSet::from_iter(accessible_roll_locations(
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&parse_roll_locations(EXAMPLE_INPUT).unwrap()
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)),
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parse_roll_locations(EXAMPLE_ACCESSIBLE_ROLLS).unwrap()
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);
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}
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#[test]
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fn non_removable_rolls_in_example() {
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assert_eq!(
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non_removable_roll_locations(parse_roll_locations(EXAMPLE_INPUT).unwrap()),
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parse_roll_locations(EXAMPLE_NON_REMOVABLE_ROLLS).unwrap()
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)
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}
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}
+2
-2
aoc_2025/src/main.rs
+2
-2
aoc_2025/src/main.rs
···
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mod day01;
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mod day02;
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mod day03;
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// mod day04;
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mod day04;
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// mod day05;
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// mod day06;
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// mod day07;
···
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door!(2025-12-01 ~> day01),
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door!(2025-12-02 ~> day02),
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door!(2025-12-03 ~> day03),
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// door!(2025-12-04 ~> day04),
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door!(2025-12-04 ~> day04),
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// door!(2025-12-05 ~> day05),
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// door!(2025-12-06 ~> day06),
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// door!(2025-12-07 ~> day07),