day(18): use tricks from day(10) to solve part 2
Signed-off-by: Matej Focko <me@mfocko.xyz>
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1 changed files with 31 additions and 56 deletions
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@ -1,6 +1,7 @@
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use std::{collections::VecDeque, str::FromStr};
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use itertools::iproduct;
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use std::{
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collections::BTreeMap,
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str::FromStr,
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};
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use aoc_2023::*;
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@ -48,73 +49,47 @@ impl Step {
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}
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}
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fn flood_fill(m: &mut [Vec<char>], start: Vector2D<isize>, original: char, fill: char) -> usize {
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let mut filled_in = 0;
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let mut q: VecDeque<Vector2D<isize>> = VecDeque::from([start]);
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m[start] = fill;
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filled_in += 1;
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while let Some(p) = q.pop_front() {
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for (dx, dy) in [(0, 1), (0, -1), (1, 0), (-1, 0)] {
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let neighbour = p + Vector2D::new(dx, dy);
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if !in_range(m, &neighbour) || m[neighbour] != original {
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continue;
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fn dir_to_u8(u: (isize, isize)) -> u8 {
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match u {
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(0, 1) => 1,
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(0, -1) => 2,
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(1, 0) => 4,
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(-1, 0) => 8,
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_ => unreachable!(),
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}
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}
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q.push_back(neighbour);
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m[neighbour] = fill;
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filled_in += 1;
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}
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}
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filled_in
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fn opposite(u: (isize, isize)) -> (isize, isize) {
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(-u.0, -u.1)
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}
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fn solve(plan: &[Step]) -> usize {
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let (min_x, max_x, min_y, max_y) = plan.iter().fold((0, 0, 0, 0), |dimensions, s| {
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let (mut lx, mut ux, mut ly, mut uy) = dimensions;
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match s._direction {
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(0, 1) => uy += s.count,
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(0, -1) => ly += s.count,
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(1, 0) => ux += s.count,
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(-1, 0) => lx += s.count,
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_ => unreachable!(),
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}
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(lx, ux, ly, uy)
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});
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let (width, height) = (min_x + max_x + 1, min_y + max_y + 1);
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debug!("Dimensions: {}×{}", width, height);
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let mut map = vec![vec!['.'; width as usize]; height as usize];
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let mut position = Vector2D::new(min_x, min_y);
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let mut hole: BTreeMap<Vector2D<isize>, u8> = BTreeMap::new();
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let mut position = Vector2D::new(0, 0);
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for s in plan.iter() {
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let direction = s.direction();
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for _ in 0..s.count {
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map[position] = '#';
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*hole.entry(position).or_insert(0) |= dir_to_u8(s._direction);
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position = position + direction;
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*hole.entry(position).or_insert(0) |= dir_to_u8(opposite(s._direction));
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}
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}
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flood_fill(&mut map, Vector2D::new(0, 0), '.', '+');
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while let Some((y, x)) =
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iproduct!(0..height as usize, 0..width as usize).find(|&(y, x)| map[y][x] == '.')
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{
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flood_fill(&mut map, Vector2D::new(x as isize, y as isize), '.', '#');
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let mut counter = 0;
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let mut in_between = 0;
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let mut x_prev = 0;
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for (v, directions) in hole.iter() {
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if in_between != 0 && x_prev < v.x() {
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// debug!("{} {}", v.x(), x_prev);
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counter += (v.x() - x_prev) as usize - 1;
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}
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in_between ^= directions & 3;
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x_prev = v.x();
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}
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// debug!(
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// "Map:\n{}",
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// map.iter().map(|r| r.iter().collect::<String>()).join("\n")
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// );
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map.iter()
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.map(|r| r.iter().filter(|&&c| c == '#').count())
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.sum()
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counter + hole.len()
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}
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struct Day18 {
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@ -150,7 +125,7 @@ impl Solution<Output1, Output2> for Day18 {
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Step {
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_direction,
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count: number >> 8,
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count: number >> 4,
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color: String::new(),
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}
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})
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