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use advent_of_code::prelude::*;
pub fn parse(fh: File) -> Result<Grid<u8>> {
Ok(parse::digit_grid(parse::raw_lines(fh)))
}
pub fn part1(map: Grid<u8>) -> Result<u64> {
let mut risk = 0;
for ((row, col), pos) in map.indexed_cells() {
if map
.adjacent(row, col, false)
.map(|(row, col)| map[row][col])
.all(|n| *pos < n)
{
risk += 1 + u64::from(*pos);
}
}
Ok(risk)
}
pub fn part2(map: Grid<u8>) -> Result<u64> {
let mut low = vec![];
for ((row, col), pos) in map.indexed_cells() {
if map
.adjacent(row, col, false)
.map(|(row, col)| map[row][col])
.all(|n| *pos < n)
{
low.push((row, col));
}
}
let mut sizes = vec![];
for (row, col) in low {
let mut basin: Grid<bool> = Grid::default();
basin.grow(map.rows(), map.cols());
let mut check = vec![(row, col)];
let mut count = 0;
while let Some((row, col)) = check.pop() {
if basin[row][col] || map[row][col] == 9 {
continue;
}
basin[row][col] = true;
count += 1;
for (row, col) in basin.adjacent(row, col, false) {
if !basin[row][col] {
check.push((row, col));
}
}
}
sizes.push(count);
}
sizes.sort_unstable();
Ok(sizes[sizes.len() - 1]
* sizes[sizes.len() - 2]
* sizes[sizes.len() - 3])
}
#[test]
fn test() {
assert_eq!(
part1(parse(parse::data(2021, 9).unwrap()).unwrap()).unwrap(),
570
);
assert_eq!(
part2(parse(parse::data(2021, 9).unwrap()).unwrap()).unwrap(),
899392
);
}
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