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2018 day 20
1 parent 842a20f commit df299e3

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‎crates/utils/src/lib.rs‎

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@@ -18,6 +18,7 @@ pub mod multiversion;
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pub mod number;
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pub mod parser;
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pub mod simd;
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pub mod slice;
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#[cfg(target_family = "wasm")]
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pub mod wasm;
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‎crates/utils/src/slice.rs‎

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@@ -0,0 +1,107 @@
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//! Slice helpers.
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use std::cmp::Ordering;
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/// Merges a sorted deduped [`Vec`] in place with a sorted deduped slice.
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///
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/// This is equivalent to a set union on sorted data.
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///
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/// Both inputs **must** be sorted and contain no duplicates.
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///
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/// # Examples
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/// ```
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/// # use utils::slice::merge_sorted_deduped_in_place;
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/// let mut v = vec![1, 3, 5];
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/// merge_sorted_deduped_in_place(&mut v, &[2, 3, 4]);
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/// assert_eq!(v, [1, 2, 3, 4, 5]);
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///
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/// // Elements at start and end
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/// let mut v = vec![1, 2, 3, 4, 5];
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/// merge_sorted_deduped_in_place(&mut v, &[0, 6]);
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/// assert_eq!(v, [0, 1, 2, 3, 4, 5, 6]);
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///
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/// // Complete overlap
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/// let mut v = vec![1, 2, 3];
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/// merge_sorted_deduped_in_place(&mut v, &[1, 2, 3]);
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/// assert_eq!(v, [1, 2, 3]);
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///
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/// // No overlap
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/// let mut v = vec![1, 2];
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/// merge_sorted_deduped_in_place(&mut v, &[3, 4]);
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/// assert_eq!(v, [1, 2, 3, 4]);
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///
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/// let mut v = vec![24, 53];
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/// merge_sorted_deduped_in_place(&mut v, &[6]);
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/// assert_eq!(v, [6, 24, 53]);
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///
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/// // Partial overlap
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/// let mut v = vec![10, 11, 12, 13];
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/// merge_sorted_deduped_in_place(&mut v, &[13, 14]);
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/// assert_eq!(v, [10, 11, 12, 13, 14]);
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///
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/// let mut v = vec![300, 400, 500];
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/// merge_sorted_deduped_in_place(&mut v, &[100, 200, 300]);
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/// assert_eq!(v, [100, 200, 300, 400, 500]);
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///
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/// // Empty inputs
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/// let mut v = Vec::new();
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/// merge_sorted_deduped_in_place(&mut v, &[5]);
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/// assert_eq!(v, [5]);
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///
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/// let mut v = vec![6];
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/// merge_sorted_deduped_in_place(&mut v, &[]);
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/// assert_eq!(v, [6]);
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///
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/// let mut v: Vec<u32> = Vec::new();
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/// merge_sorted_deduped_in_place(&mut v, &[]);
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/// assert_eq!(v, []);
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/// ```
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#[inline]
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pub fn merge_sorted_deduped_in_place<T: Copy + Ord + Default>(a: &mut Vec<T>, b: &[T]) {
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debug_assert!(a.windows(2).all(|w| w[0] < w[1]));
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debug_assert!(b.windows(2).all(|w| w[0] < w[1]));
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let mut new = 0;
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let (mut i, mut j) = (0, 0);
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while i < a.len() && j < b.len() {
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match a[i].cmp(&b[j]) {
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Ordering::Less => i += 1,
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Ordering::Equal => {
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i += 1;
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j += 1;
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}
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Ordering::Greater => {
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new += 1;
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j += 1;
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}
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}
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}
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new += b.len() - j;
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if new == 0 {
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return;
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}
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let (mut i, mut j, mut write) = (a.len(), b.len(), a.len() + new);
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a.resize(a.len() + new, T::default());
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while i > 0 && j > 0 {
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write -= 1;
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a[write] = match a[i - 1].cmp(&b[j - 1]) {
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Ordering::Less => {
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j -= 1;
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b[j]
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}
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Ordering::Equal => {
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i -= 1;
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j -= 1;
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a[i]
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}
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Ordering::Greater => {
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i -= 1;
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a[i]
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}
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}
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}
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a[..j].copy_from_slice(&b[..j]);
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}

‎crates/year2018/src/day20.rs‎

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use utils::prelude::*;
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use utils::slice::merge_sorted_deduped_in_place;
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/// Following a regex’s branching paths within a grid.
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#[derive(Clone, Debug)]
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pub struct Day20 {
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part1: u16,
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part2: u16,
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}
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const WIDTH: usize = 109;
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impl Day20 {
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pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
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if input.as_bytes().first() != Some(&b'^') {
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return Err(InputError::new(input, 0, "expected '^'"));
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}
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if input.as_bytes().last() != Some(&b'$') {
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return Err(InputError::new(input, input.len() - 1, "expected '$'"));
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}
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let mut grid = [0u16; WIDTH * WIDTH];
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let mut positions = vec![(WIDTH * WIDTH) / 2];
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let (mut start, mut end) = (Vec::new(), Vec::new());
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let mut stack = Vec::with_capacity(256);
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for (i, &b) in input.as_bytes()[..input.len() - 1]
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.iter()
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.enumerate()
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.skip(1)
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{
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let dir = match b {
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b'N' => -(WIDTH as isize),
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b'E' => 1,
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b'S' => WIDTH as isize,
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b'W' => -1,
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b'(' => {
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stack.push((std::mem::take(&mut start), std::mem::take(&mut end)));
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start.clone_from(&positions);
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continue;
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}
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b'|' => {
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if stack.is_empty() {
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return Err(InputError::new(input, i, "unexpected '|'"));
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}
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merge_sorted_deduped_in_place(&mut end, &positions);
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positions.clone_from(&start);
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continue;
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}
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b')' => {
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merge_sorted_deduped_in_place(&mut positions, &end);
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let Some(entry) = stack.pop() else {
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return Err(InputError::new(input, i, "unexpected ')'"));
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};
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(start, end) = entry;
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continue;
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}
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_ => {
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return Err(InputError::new(
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input,
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i,
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"expected 'N', 'E', 'S', 'W', '(', '|' or ')'",
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));
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}
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};
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for p in positions.iter_mut() {
73+
let distance = grid[*p];
74+
*p = p.wrapping_add_signed(dir);
75+
if grid[*p] == 0 || distance + 1 < grid[*p] {
76+
grid[*p] = distance + 1;
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}
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}
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}
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if !stack.is_empty() {
82+
return Err(InputError::new(input, input.len() - 1, "expected ')'"));
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}
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Ok(Self {
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part1: grid.iter().max().copied().unwrap_or(0),
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part2: grid.iter().filter(|&&d| d >= 1000).count() as u16,
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})
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}
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#[must_use]
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pub fn part1(&self) -> u16 {
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self.part1
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}
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#[must_use]
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pub fn part2(&self) -> u16 {
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self.part2
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}
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}
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examples!(Day20 -> (u16, u16) [
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{input: "^WNE$", part1: 3},
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{input: "^ENWWW(NEEE|SSE(EE|N))$", part1: 10},
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{input: "^ENNWSWW(NEWS|)SSSEEN(WNSE|)EE(SWEN|)NNN$", part1: 18},
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{input: "^ESSWWN(E|NNENN(EESS(WNSE|)SSS|WWWSSSSE(SW|NNNE)))$", part1: 23},
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{input: "^WSSEESWWWNW(S|NENNEEEENN(ESSSSW(NWSW|SSEN)|WSWWN(E|WWS(E|SS))))$", part1: 31},
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]);

‎crates/year2018/src/lib.rs‎

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@@ -21,4 +21,5 @@ utils::year!(2018 => year2018, ${
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17 => day17::Day17,
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18 => day18::Day18,
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19 => day19::Day19,
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20 => day20::Day20,
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});

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