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|
use nom::{
branch::alt,
bytes::complete::tag,
character::complete::line_ending,
combinator::{map, value},
multi::{many1, separated_list1},
IResult,
};
use std::{
collections::{BTreeMap, BTreeSet, VecDeque},
fs,
};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_23_test.txt")?;
let mut elves = ElfMap::parser(&input).unwrap().1;
dbg!(&elves);
for _ in 0..10 {
elves.process_round();
dbg!(&elves);
}
dbg!(elves.count_empty_ground());
Ok(())
}
#[derive(Debug, Clone)]
struct ElfMap {
elves: BTreeSet<Point>,
check_order: VecDeque<Direction>,
}
#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point {
y: i64,
x: i64,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum Direction {
North,
South,
West,
East,
}
impl ElfMap {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(
line_ending,
map(
many1(alt((value(true, tag("#")), value(false, tag("."))))),
|row| {
row.into_iter()
.enumerate()
.filter_map(|(x, occupied)| occupied.then_some(x as i64))
.collect::<Vec<i64>>()
},
),
),
|rows| {
let elves = rows
.into_iter()
.enumerate()
.flat_map(|(y, row)| row.into_iter().map(move |x| Point { x, y: y as i64 }))
.collect();
ElfMap {
elves,
check_order: [
Direction::North,
Direction::South,
Direction::West,
Direction::East,
]
.into(),
}
},
)(input)
}
fn process_round(&mut self) {
// key is destination!
let mut elf_moves: BTreeMap<Point, Point> = BTreeMap::new();
let mut conflict_moves: BTreeSet<Point> = BTreeSet::new();
// phase 1: figure out where each elf wants to move
for elf in &self.elves {
if let Some(destination) = self.find_elf_move(&elf) {
if elf_moves.contains_key(&destination) {
elf_moves.remove(&destination);
conflict_moves.insert(destination);
} else if !conflict_moves.contains(&destination) {
elf_moves.insert(destination, elf.clone());
}
}
}
// phase 2: move the elves
for (dest, src) in elf_moves {
self.elves.remove(&src);
self.elves.insert(dest);
}
let rotate = self
.check_order
.pop_front()
.expect("Where did the directions go?");
self.check_order.push_back(rotate);
}
fn find_elf_move(&self, elf: &Point) -> Option<Point> {
let all_adjacent = elf.adjacent(None);
let any_adjacent_elves = all_adjacent.into_iter().any(|p| self.elves.contains(&p));
if !any_adjacent_elves {
None
} else {
self.check_order
.iter()
.filter_map(|dir| {
let adjacent = elf.adjacent(Some(*dir));
let any_adjacent_elves = adjacent.iter().any(|p| self.elves.contains(p));
if !any_adjacent_elves {
Some(adjacent[1].clone())
} else {
None
}
})
.next()
}
}
fn count_empty_ground(&self) -> i64 {
let mut min_x = 0;
let mut min_y = 0;
let mut max_x = 0;
let mut max_y = 0;
for elf in &self.elves {
min_x = min_x.min(elf.x);
min_y = min_y.min(elf.y);
max_x = max_x.max(elf.x);
max_y = max_y.max(elf.y);
}
let all_ground = (max_x - min_x + 1) * (max_y - min_y + 1);
let covered_ground = self.elves.len() as i64;
all_ground - covered_ground
}
}
impl Point {
fn adjacent(&self, direction: Option<Direction>) -> Vec<Point> {
let (y_range, x_range) = match direction {
None => ((-1..=1), (-1..=1)),
Some(Direction::North) => ((-1..=-1), (-1..=1)),
Some(Direction::South) => ((1..=1), (-1..=1)),
Some(Direction::East) => ((-1..=1), (-1..=-1)),
Some(Direction::West) => ((-1..=1), (1..=1)),
};
y_range
.flat_map(|dy| {
x_range.clone().map(move |dx| Point {
x: self.x + dx,
y: self.y + dy,
})
})
.filter(|p| p != self)
.collect()
}
}
|
