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|
use nom::{
branch::alt,
character::complete::{char, line_ending},
combinator::{map, value},
multi::{many1, separated_list1},
IResult,
};
use std::{collections::BTreeSet, fs, mem};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_21.txt")?;
let mut walled_garden = WalledGarden::parser(&input).unwrap().1;
for _ in 0..64 {
walled_garden = walled_garden.next();
}
dbg!(&walled_garden.count_walkable());
let mut open_garden = OpenGarden::parser(&input).unwrap().1;
// - the paths straight up / down, and left / right from the middle and edges are clear.
// - this would allow finding a "single tile" version (eg part 1) to see how much of a tile could be filled at the boundaries.
// - start at the top boundary I can get into, 26501365 / 131
// - when I find a fully explored garden, I can extrapolate that any closer gardens are also filled out
// - for filled out gardens, there will be an 'even' and an 'odd' answer (alternating checkerboard). choose the right one to add it.
// - this is still around 202300 pages in each direction, so multiplying the rows etc seems like a good idea. Eg do the two sides, then multiply out the fully explored middle.
let open_iters = 26501365;
for i in 0..open_iters {
if i % 100000 == 0 {
println!("{}", i as f32 / open_iters as f32);
}
open_garden.next_mut();
}
dbg!(&open_garden.count_walkable());
Ok(())
}
#[derive(Debug)]
struct WalledGarden(Vec<Vec<WalledGardenState>>);
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum WalledGardenState {
Empty,
Walkable,
Rock,
}
impl WalledGarden {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(line_ending, many1(WalledGardenState::parser)),
WalledGarden,
)(input)
}
fn next(&self) -> WalledGarden {
WalledGarden(
(0..self.0.len() as isize)
.map(|y| {
(0..self.0[y as usize].len() as isize)
.map(|x| {
let current = self.get(y, x);
let neighbours = [
self.get(y - 1, x),
self.get(y + 1, x),
self.get(y, x - 1),
self.get(y, x + 1),
];
if current == WalledGardenState::Rock {
WalledGardenState::Rock
} else if neighbours.contains(&WalledGardenState::Walkable) {
WalledGardenState::Walkable
} else {
WalledGardenState::Empty
}
})
.collect::<Vec<WalledGardenState>>()
})
.collect(),
)
}
fn get(&self, y: isize, x: isize) -> WalledGardenState {
if y < 0 || x < 0 {
WalledGardenState::Rock
} else {
let y = y as usize;
let x = x as usize;
if y >= self.0.len() || x >= self.0[y].len() {
WalledGardenState::Rock
} else {
self.0[y][x]
}
}
}
fn count_walkable(&self) -> usize {
self.0
.iter()
.flat_map(|row| row.iter())
.filter(|s| **s == WalledGardenState::Walkable)
.count()
}
}
impl WalledGardenState {
fn parser(input: &str) -> IResult<&str, Self> {
alt((
value(WalledGardenState::Empty, char('.')),
value(WalledGardenState::Walkable, char('S')),
value(WalledGardenState::Rock, char('#')),
))(input)
}
}
#[derive(Debug)]
struct OpenGarden {
rockmap_size: (isize, isize),
rocks: BTreeSet<(isize, isize)>,
walkable: BTreeSet<(isize, isize)>,
}
impl OpenGarden {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(line_ending, many1(WalledGardenState::parser)),
|walled_garden_map| OpenGarden {
rockmap_size: (
walled_garden_map.len() as isize,
walled_garden_map[0].len() as isize,
),
rocks: walled_garden_map
.iter()
.enumerate()
.flat_map(|(y, row)| {
row.iter().enumerate().filter_map(move |(x, s)| {
(*s == WalledGardenState::Rock).then(|| (y as isize, x as isize))
})
})
.collect(),
walkable: walled_garden_map
.iter()
.enumerate()
.flat_map(|(y, row)| {
row.iter().enumerate().filter_map(move |(x, s)| {
(*s == WalledGardenState::Walkable).then(|| (y as isize, x as isize))
})
})
.collect(),
},
)(input)
}
fn next_mut(&mut self) {
let walkable = mem::take(&mut self.walkable);
self.walkable = walkable
.iter()
.flat_map(|(y, x)| [(y - 1, *x), (y + 1, *x), (*y, x - 1), (*y, x + 1)])
.filter(|(y, x)| !self.is_rock(*y, *x))
.collect();
}
fn is_rock(&self, y: isize, x: isize) -> bool {
let y = y.rem_euclid(self.rockmap_size.0);
let x = x.rem_euclid(self.rockmap_size.1);
self.rocks.contains(&(y, x))
}
fn count_walkable(&self) -> usize {
self.walkable.len()
}
}
|
