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use crate::util::grid::*;
pub struct Map {
grid: Grid<bool>,
}
impl Map {
fn new(grid: Grid<bool>) -> Self {
Self { grid }
}
fn rows(&self) -> usize {
self.grid.rows().0
}
fn tree_at(&self, row: Row, col: Col) -> anyhow::Result<bool> {
// unwrap safe because cycle().nth() can never fail
Ok(*self.grid[row].iter().cycle().nth(col.0).unwrap())
}
fn trees_for_slope(
&self,
row_incr: usize,
col_incr: usize,
) -> anyhow::Result<i64> {
let mut trees = 0;
for r in 0..self.rows() / row_incr {
let row = r * row_incr;
let col = r * col_incr;
if self.tree_at(Row(row), Col(col))? {
trees += 1;
}
}
Ok(trees)
}
}
pub fn parse(fh: std::fs::File) -> anyhow::Result<Map> {
Ok(Map::new(crate::util::parse::bool_grid(
crate::util::parse::lines(fh),
b'#',
b'.',
)))
}
pub fn part1(map: Map) -> anyhow::Result<i64> {
map.trees_for_slope(1, 3)
}
pub fn part2(map: Map) -> anyhow::Result<i64> {
Ok(map.trees_for_slope(1, 1)?
* map.trees_for_slope(1, 3)?
* map.trees_for_slope(1, 5)?
* map.trees_for_slope(1, 7)?
* map.trees_for_slope(2, 1)?)
}
#[test]
fn test() {
assert_eq!(
part1(parse(crate::util::data(2020, 3).unwrap()).unwrap()).unwrap(),
292
);
assert_eq!(
part2(parse(crate::util::data(2020, 3).unwrap()).unwrap()).unwrap(),
9354744432
);
}
|
