2020: day03: part 2

This commit is contained in:
Antoine Martin 2020-12-03 17:36:19 +01:00
parent 389693dabc
commit 37e653b782

View file

@ -9,6 +9,7 @@ pub fn run() -> aoc::Result<String> {
let mut res = String::with_capacity(128); let mut res = String::with_capacity(128);
writeln!(res, "part 1: {}", part1(INPUT)?)?; writeln!(res, "part 1: {}", part1(INPUT)?)?;
writeln!(res, "part 2: {}", part2(INPUT)?)?;
Ok(res) Ok(res)
} }
@ -19,11 +20,25 @@ fn part1(input: &str) -> aoc::Result<usize> {
Ok(count_trees(&forest, (3, 1))) Ok(count_trees(&forest, (3, 1)))
} }
fn part2(input: &str) -> aoc::Result<usize> {
let forest = input.parse()?;
let slopes = &[(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)];
Ok(slopes
.iter()
.map(|slope| count_trees(&forest, *slope))
.product())
}
fn count_trees(forest: &Forest, (right, down): (usize, usize)) -> usize { fn count_trees(forest: &Forest, (right, down): (usize, usize)) -> usize {
let vertical_range = (0..forest.height()).step_by(down); let vertical_range = (0..forest.height()).step_by(down);
let horizontal_range = (0..).step_by(right); let horizontal_range = (0..).step_by(right);
vertical_range.zip(horizontal_range).filter(|(i, j)| forest[*i][*j]).count() vertical_range
.zip(horizontal_range)
.filter(|(i, j)| forest[*i][*j])
.count()
} }
#[derive(Debug)] #[derive(Debug)]
@ -101,4 +116,22 @@ mod tests {
fn part1_real() { fn part1_real() {
assert_eq!(part1(INPUT).unwrap(), 242); assert_eq!(part1(INPUT).unwrap(), 242);
} }
#[test]
fn part2_provided() {
let forest = PROVIDED.parse().unwrap();
assert_eq!(count_trees(&forest, (1, 1)), 2);
assert_eq!(count_trees(&forest, (3, 1)), 7);
assert_eq!(count_trees(&forest, (5, 1)), 3);
assert_eq!(count_trees(&forest, (7, 1)), 4);
assert_eq!(count_trees(&forest, (1, 2)), 2);
assert_eq!(part2(PROVIDED).unwrap(), 336);
}
#[test]
fn part2_real() {
assert_eq!(part2(INPUT).unwrap(), 2265549792);
}
} }