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day(18): use tricks from day(10) to solve part 2

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Signed-off-by: Matej Focko <me@mfocko.xyz>
This commit is contained in:
Matej Focko 2023-12-18 19:21:41 +01:00
parent 69287d8a30
commit 9a5d814792
Signed by: mfocko
GPG key ID: 7C47D46246790496
1 changed files with 31 additions and 56 deletions
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85
src/bin/day18.rs
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@ -1,6 +1,7 @@
use std::{collections::VecDeque, str::FromStr};
use itertools::iproduct;
use std::{
collections::BTreeMap,
str::FromStr,
};
use aoc_2023::*;
@ -48,73 +49,47 @@ impl Step {
}
}
fn flood_fill(m: &mut [Vec<char>], start: Vector2D<isize>, original: char, fill: char) -> usize {
let mut filled_in = 0;
let mut q: VecDeque<Vector2D<isize>> = VecDeque::from([start]);
m[start] = fill;
filled_in += 1;
while let Some(p) = q.pop_front() {
for (dx, dy) in [(0, 1), (0, -1), (1, 0), (-1, 0)] {
let neighbour = p + Vector2D::new(dx, dy);
if !in_range(m, &neighbour) || m[neighbour] != original {
continue;
}
q.push_back(neighbour);
m[neighbour] = fill;
filled_in += 1;
fn dir_to_u8(u: (isize, isize)) -> u8 {
match u {
(0, 1) => 1,
(0, -1) => 2,
(1, 0) => 4,
(-1, 0) => 8,
_ => unreachable!(),
}
}
filled_in
fn opposite(u: (isize, isize)) -> (isize, isize) {
(-u.0, -u.1)
}
fn solve(plan: &[Step]) -> usize {
let (min_x, max_x, min_y, max_y) = plan.iter().fold((0, 0, 0, 0), |dimensions, s| {
let (mut lx, mut ux, mut ly, mut uy) = dimensions;
match s._direction {
(0, 1) => uy += s.count,
(0, -1) => ly += s.count,
(1, 0) => ux += s.count,
(-1, 0) => lx += s.count,
_ => unreachable!(),
}
(lx, ux, ly, uy)
});
let (width, height) = (min_x + max_x + 1, min_y + max_y + 1);
debug!("Dimensions: {}×{}", width, height);
let mut map = vec![vec!['.'; width as usize]; height as usize];
let mut position = Vector2D::new(min_x, min_y);
let mut hole: BTreeMap<Vector2D<isize>, u8> = BTreeMap::new();
let mut position = Vector2D::new(0, 0);
for s in plan.iter() {
let direction = s.direction();
for _ in 0..s.count {
map[position] = '#';
*hole.entry(position).or_insert(0) |= dir_to_u8(s._direction);
position = position + direction;
*hole.entry(position).or_insert(0) |= dir_to_u8(opposite(s._direction));
}
}
flood_fill(&mut map, Vector2D::new(0, 0), '.', '+');
while let Some((y, x)) =
iproduct!(0..height as usize, 0..width as usize).find(|&(y, x)| map[y][x] == '.')
{
flood_fill(&mut map, Vector2D::new(x as isize, y as isize), '.', '#');
let mut counter = 0;
let mut in_between = 0;
let mut x_prev = 0;
for (v, directions) in hole.iter() {
if in_between != 0 && x_prev < v.x() {
// debug!("{} {}", v.x(), x_prev);
counter += (v.x() - x_prev) as usize - 1;
}
in_between ^= directions & 3;
x_prev = v.x();
}
// debug!(
// "Map:\n{}",
// map.iter().map(|r| r.iter().collect::<String>()).join("\n")
// );
map.iter()
.map(|r| r.iter().filter(|&&c| c == '#').count())
.sum()
counter + hole.len()
}
struct Day18 {
@ -150,7 +125,7 @@ impl Solution<Output1, Output2> for Day18 {
Step {
_direction,
count: number >> 8,
count: number >> 4,
color: String::new(),
}
})