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use crate::prelude::*;
fn iterate(grid: &mut Grid<(u8, bool)>) -> i64 {
let mut flashes = 0;
for (cell, _) in grid.cells_mut() {
*cell += 1;
}
loop {
let mut new_flashes = 0;
let mut updates: Grid<u8> = Grid::default();
updates.grow(grid.rows(), grid.cols());
for ((row, col), (cell, flashed)) in grid.indexed_cells_mut() {
if *flashed {
continue;
}
if *cell > 9 {
*flashed = true;
new_flashes += 1;
for (row, col) in updates.adjacent(row, col, true) {
updates[row][col] += 1;
}
}
}
if new_flashes > 0 {
flashes += new_flashes;
for ((row, col), val) in updates.indexed_cells() {
grid[row][col].0 += val;
}
} else {
break;
}
}
for (cell, flashed) in grid.cells_mut() {
if *flashed {
*cell = 0;
*flashed = false;
}
}
flashes
}
pub fn parse(fh: File) -> Result<Grid<(u8, bool)>> {
Ok(parse::digit_grid(parse::lines(fh))
.indexed_cells()
.map(|((row, col), cell)| ((row, col), (*cell, false)))
.collect())
}
pub fn part1(mut map: Grid<(u8, bool)>) -> Result<i64> {
let mut flashes = 0;
for _ in 0..100 {
flashes += iterate(&mut map);
}
Ok(flashes)
}
pub fn part2(mut map: Grid<(u8, bool)>) -> Result<i64> {
let mut step = 1;
loop {
let flashes = iterate(&mut map);
if flashes == (map.rows().0 * map.cols().0).try_into()? {
break;
}
step += 1;
}
Ok(step)
}
#[test]
fn test() {
assert_eq!(
part1(parse(parse::data(2021, 11).unwrap()).unwrap()).unwrap(),
1673
);
assert_eq!(
part2(parse(parse::data(2021, 11).unwrap()).unwrap()).unwrap(),
279
);
}
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