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|
use nom::{
bytes::complete::tag,
character::complete::{i32, line_ending},
combinator::map,
multi::separated_list1,
sequence::tuple,
IResult,
};
use std::{collections::BTreeSet, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_18.txt")?;
let voxels = Voxels::parser(&input).unwrap().1;
dbg!(voxels.naive_surface_area());
dbg!(voxels.exterior_surface_area());
Ok(())
}
#[derive(Debug, Clone)]
struct Voxels(BTreeSet<Point3d>);
#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point3d {
x: i32,
y: i32,
z: i32,
}
impl Voxels {
fn parser(input: &str) -> IResult<&str, Self> {
map(separated_list1(line_ending, Point3d::parser), |vox| {
Voxels(vox.into_iter().collect())
})(input)
}
fn naive_surface_area(&self) -> usize {
let units = Point3d::units();
self.0
.iter()
.flat_map(|v| units.iter().map(move |u| v + u))
.filter(|v| !self.0.contains(v))
.count()
}
fn exterior_surface_area(&self) -> usize {
let units = Point3d::units();
let mut known_internal: BTreeSet<Point3d> = BTreeSet::new();
let known_external = self.bounds();
self.0
.iter()
.flat_map(|v| units.iter().map(move |u| v + u))
.filter(|v| !self.0.contains(v))
.filter(|v| {
if known_internal.contains(v) {
return false;
}
let mut flooded: BTreeSet<Point3d> = BTreeSet::new();
let mut frontier: BTreeSet<Point3d> = BTreeSet::new();
flooded.insert(v.clone());
frontier.insert(v.clone());
let mut is_internal = true;
while is_internal && frontier.len() > 0 {
let mut next_frontier = BTreeSet::new();
for front in &frontier {
for unit in &units {
let adjacent = front + unit;
if !self.0.contains(&adjacent) && !flooded.contains(&adjacent) {
if known_external.contains(&adjacent) {
is_internal = false;
}
flooded.insert(adjacent.clone());
next_frontier.insert(adjacent);
}
}
}
frontier = next_frontier;
}
if is_internal {
known_internal.append(&mut flooded);
}
!is_internal
})
.count()
}
fn bounds(&self) -> BTreeSet<Point3d> {
let min_x = self.0.iter().map(|v| v.x).min().unwrap_or(0) - 1;
let max_x = self.0.iter().map(|v| v.x).max().unwrap_or(0) + 1;
let min_y = self.0.iter().map(|v| v.y).min().unwrap_or(0) - 1;
let max_y = self.0.iter().map(|v| v.y).max().unwrap_or(0) + 1;
let min_z = self.0.iter().map(|v| v.z).min().unwrap_or(0) - 1;
let max_z = self.0.iter().map(|v| v.z).max().unwrap_or(0) + 1;
let mut result = BTreeSet::new();
for x in [min_x, max_x] {
for y in [min_y, max_y] {
for z in [min_z, max_z] {
result.insert(Point3d { x, y, z });
}
}
}
result
}
}
impl Point3d {
fn parser(input: &str) -> IResult<&str, Self> {
map(
tuple((i32, tag(","), i32, tag(","), i32)),
|(x, _, y, _, z)| Point3d { x, y, z },
)(input)
}
fn units() -> Vec<Point3d> {
vec![
Point3d {
x: -1,
..Point3d::default()
},
Point3d {
x: 1,
..Point3d::default()
},
Point3d {
y: -1,
..Point3d::default()
},
Point3d {
y: 1,
..Point3d::default()
},
Point3d {
z: -1,
..Point3d::default()
},
Point3d {
z: 1,
..Point3d::default()
},
]
}
}
impl ::core::ops::Add<&Point3d> for &Point3d {
type Output = Point3d;
fn add(self, rhs: &Point3d) -> Point3d {
Point3d {
x: self.x.add(rhs.x),
y: self.y.add(rhs.y),
z: self.z.add(rhs.z),
}
}
}
|
