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use std::collections::HashMap;
fn main() {
let input = advent::read_lines(18);
println!("18a: {}", count_lights(&input, 100, false));
println!("18b: {}", count_lights(&input, 100, true));
}
fn count_neighbors(grid: &HashMap<(isize, isize), bool>, pos: (isize, isize)) -> usize {
let mut count = 0;
for x in pos.0 - 1 ..= pos.0 + 1 {
for y in pos.1 - 1 ..= pos.1 + 1 {
if (x, y) == pos {
continue;
}
if let Some(true) = grid.get(&(x, y)) {
count += 1;
}
}
}
count
}
fn stuck_grid(grid: &mut HashMap<(isize, isize), bool>, dim: isize) {
grid.insert((0, 0), true);
grid.insert((dim-1, dim-1), true);
grid.insert((0, dim-1), true);
grid.insert((dim-1, 0), true);
}
fn step(grid: HashMap<(isize, isize), bool>, dim: usize, stuck: bool) -> HashMap<(isize, isize), bool> {
let mut next_grid = HashMap::new();
for y in 0 .. dim {
for x in 0 .. dim {
let pos = (x as isize, y as isize);
let val = *grid.get(&pos).unwrap();
let neighbors = count_neighbors(&grid, pos);
let new_val = match val {
true => [2, 3].contains(&neighbors),
false => neighbors == 3,
};
next_grid.insert(pos, new_val);
}
}
if stuck {
stuck_grid(&mut next_grid, dim as isize);
}
next_grid
}
fn count_lights(input: &[String], steps: u16, stuck: bool) -> usize {
let dim = input.len();
let mut grid = HashMap::new();
for (y, line) in input.iter().enumerate() {
for (x, c) in line.chars().enumerate() {
let pos = (x as isize, y as isize);
match c {
'#' => grid.insert(pos, true),
'.' => grid.insert(pos, false),
_ => unimplemented!(),
};
}
}
if stuck {
stuck_grid(&mut grid, dim as isize);
}
for _ in 0 .. steps {
grid = step(grid, dim, stuck);
}
grid.values().filter(|&val| *val).count()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
".#.#.#".to_string(),
"...##.".to_string(),
"#....#".to_string(),
"..#...".to_string(),
"#.#..#".to_string(),
"####..".to_string(),
];
assert_eq!(count_lights(&input, 4, false), 4);
assert_eq!(count_lights(&input, 5, true), 17);
}
}
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