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use advent_lib::prelude::*;
fn main() -> Result<()> {
let mut args = std::env::args();
if args.len() != 2 {
eprintln!("Usage: advent input");
}
let _ = args.next();
let filename = args.next().unwrap();
let input = advent_lib::read_lines_file(&filename)?;
let mut grid = Vec::new();
for line in &input {
let mut row = Vec::new();
for c in line.chars() {
let value: i64 = c.to_digit(10).unwrap() as i64;
row.push(value);
}
grid.push(row);
}
let mut n_flashes = 0;
for _ in 0 .. 100 {
n_flashes += iterate(&mut grid);
}
println!("{}", n_flashes);
for i in 101 .. 1000000 {
if iterate(&mut grid) == 100 {
println!("{}", i);
break;
}
}
Ok(())
}
#[allow(dead_code)]
fn debug_grid(grid: &Vec<Vec<i64>>) {
for row in grid {
for cell in row {
print!(" {}", cell)
}
println!("");
}
println!("");
}
fn iterate(grid: &mut Vec<Vec<i64>>) -> i64 {
let height = grid.len();
let width = grid[0].len();
let mut has_flashed = Vec::new();
for _ in 0 .. height {
let mut has_flashed_row = Vec::new();
for _ in 0 .. width {
has_flashed_row.push(false);
}
has_flashed.push(has_flashed_row);
}
for y in 0 .. height {
for x in 0 .. width {
grid[y][x] += 1;
}
}
let mut n_flashes = 0;
loop {
let mut any_flashes = false;
for y in 0 .. height {
for x in 0 .. width {
if (grid[y][x] > 9) && !has_flashed[y][x] {
n_flashes += 1;
has_flashed[y][x] = true;
any_flashes = true;
for (dx, dy) in &[(-1, -1), (0, -1), (1, -1),
(-1, 0), (1, 0),
(-1, 1), (0, 1), (1, 1)]
{
let adjacent_x = x as i64 + dx;
let adjacent_y = y as i64 + dy;
if (adjacent_x >= 0) && (adjacent_x < width as i64)
&& (adjacent_y >= 0) && (adjacent_y < height as i64)
{
grid[adjacent_y as usize][adjacent_x as usize] += 1;
}
}
}
}
}
if !any_flashes {
break;
}
}
for y in 0 .. height {
for x in 0 .. width {
if has_flashed[y][x] {
grid[y][x] = 0;
}
}
}
n_flashes
}
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