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use std::collections::{HashSet, HashMap};
static DAY: u8 = 23;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", ground_tiles(&input));
println!("{DAY}b: {}", no_movement(&input));
}
struct Map {
elves: HashSet<(isize,isize)>,
proposed: HashMap<(isize,isize), usize>,
rounds: usize,
}
impl Map {
fn new(input: &[String]) -> Map {
let mut elves = HashSet::new();
for (y, line) in input.iter().enumerate() {
for (x, symbol) in line.chars().enumerate() {
if symbol == '#' {
elves.insert((x as isize, y as isize));
}
}
}
Map { elves, proposed: HashMap::new(), rounds: 0 }
}
fn has_neighbors(&self, pos: (isize, isize), direction: Option<usize>) -> bool {
let (x,y) = pos;
match direction {
Some(0) => self.elves.contains(&(x-1,y-1)) || self.elves.contains(&(x,y-1)) || self.elves.contains(&(x+1,y-1)),
Some(1) => self.elves.contains(&(x-1,y+1)) || self.elves.contains(&(x,y+1)) || self.elves.contains(&(x+1,y+1)),
Some(2) => self.elves.contains(&(x-1,y-1)) || self.elves.contains(&(x-1,y)) || self.elves.contains(&(x-1,y+1)),
Some(3) => self.elves.contains(&(x+1,y-1)) || self.elves.contains(&(x+1,y)) || self.elves.contains(&(x+1,y+1)),
Some(_) => unimplemented!(),
None => self.has_neighbors(pos, Some(0)) || self.has_neighbors(pos, Some(1)) || self.has_neighbors(pos, Some(2)) || self.has_neighbors(pos, Some(3))
}
}
fn next_round(&mut self) {
let direction = self.rounds % 4;
/* first half */
for elf in &self.elves {
let (x,y) = *elf;
if !self.has_neighbors(*elf, None) {
continue;
}
for d in 0 .. 4 {
let d = (direction + d) % 4;
if !self.has_neighbors(*elf, Some(d)) {
match d {
0 => *self.proposed.entry((x,y-1)).or_insert(0) += 1,
1 => *self.proposed.entry((x,y+1)).or_insert(0) += 1,
2 => *self.proposed.entry((x-1,y)).or_insert(0) += 1,
3 => *self.proposed.entry((x+1,y)).or_insert(0) += 1,
_ => unimplemented!(),
};
break;
}
}
}
/* second half */
let mut new_positions = HashSet::new();
for elf in &self.elves {
let (x,y) = *elf;
if !self.has_neighbors(*elf, None) {
new_positions.insert(*elf);
continue;
}
if self.has_neighbors(*elf, Some(0)) && self.has_neighbors(*elf, Some(1)) && self.has_neighbors(*elf, Some(2)) && self.has_neighbors(*elf, Some(3)) {
new_positions.insert(*elf);
continue;
}
for d in 0 .. 4 {
let d = (direction + d) % 4;
if !self.has_neighbors(*elf, Some(d)) {
match d {
0 => if *self.proposed.get(&(x,y-1)).unwrap() == 1 {
new_positions.insert((x,y-1))
} else {
new_positions.insert((x,y))
},
1 => if *self.proposed.get(&(x,y+1)).unwrap() == 1 {
new_positions.insert((x,y+1))
} else {
new_positions.insert((x,y))
},
2 => if *self.proposed.get(&(x-1,y)).unwrap() == 1 {
new_positions.insert((x-1,y))
} else {
new_positions.insert((x,y))
},
3 => if *self.proposed.get(&(x+1,y)).unwrap() == 1 {
new_positions.insert((x+1,y))
} else {
new_positions.insert((x,y))
},
_ => unimplemented!(),
};
break;
}
}
}
self.elves = new_positions;
self.proposed.clear();
self.rounds += 1;
}
fn count_ground_tiles(&self) -> usize {
let min_x = self.elves.iter().map(|e| e.0).min().unwrap();
let min_y = self.elves.iter().map(|e| e.1).min().unwrap();
let max_x = self.elves.iter().map(|e| e.0).max().unwrap();
let max_y = self.elves.iter().map(|e| e.1).max().unwrap();
((max_x.abs_diff(min_x) + 1) * (max_y.abs_diff(min_y) + 1)) - self.elves.len()
}
}
fn ground_tiles(input: &[String]) -> usize {
let mut map = Map::new(input);
for _ in 0 .. 10 {
map.next_round();
}
map.count_ground_tiles()
}
fn no_movement(input: &[String]) -> usize {
let mut map = Map::new(input);
let mut old_positions = HashSet::new();
while map.elves.difference(&old_positions).count() > 0 {
old_positions = map.elves.iter().cloned().collect();
map.next_round();
}
map.rounds
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"....#..",
"..###.#",
"#...#.#",
".#...##",
"#.###..",
"##.#.##",
".#..#..",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(ground_tiles(&input), 110);
assert_eq!(no_movement(&input), 20);
}
}
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