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day16: use tail recursion unstead of passing mutable state

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This commit is contained in:
Keenan Tims 2023-12-16 11:07:39 -08:00
parent 842def62dc
commit da25b73eca
Signed by: ktims
GPG Key ID: 11230674D69038D4
1 changed files with 22 additions and 21 deletions
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41
16/src/main.rs
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@ -41,12 +41,12 @@ enum FromDirection {
}
impl FromDirection {
fn mask(&self) -> u8 {
const fn mask(&self) -> u8 {
1 << *self as u8
}
// return the new pos for a ray that will be from the direction.
// a ray 'from' left 'goes' right
fn goes_pos(&self, pos: (i64, i64)) -> (i64, i64) {
const fn goes_pos(&self, pos: (i64, i64)) -> (i64, i64) {
match self {
Self::Left => (pos.0 + 1, pos.1),
Self::Right => (pos.0 - 1, pos.1),
@ -54,7 +54,7 @@ impl FromDirection {
Self::Below => (pos.0, pos.1 - 1),
}
}
fn reflect_ne(&self) -> Self {
const fn reflect_ne(&self) -> Self {
match self {
Self::Left => Self::Below,
Self::Right => Self::Above,
@ -62,7 +62,7 @@ impl FromDirection {
Self::Below => Self::Left,
}
}
fn opposite(&self) -> FromDirection {
const fn opposite(&self) -> FromDirection {
match self {
Self::Left => Self::Right,
Self::Right => Self::Left,
@ -70,7 +70,7 @@ impl FromDirection {
Self::Below => Self::Above,
}
}
fn reflect_se(&self) -> FromDirection {
const fn reflect_se(&self) -> FromDirection {
self.reflect_ne().opposite()
}
fn interact(&self, tile: char) -> Interaction {
@ -90,7 +90,7 @@ impl FromDirection {
Interaction::Two((FromDirection::Left, FromDirection::Right))
}
},
c => unimplemented!("invalid tile {}", c),
c => panic!("invalid tile {}", c),
}
}
}
@ -150,17 +150,15 @@ impl Contraption {
fn width(&self) -> i64 {
self.tiles[0].len() as i64
}
fn cast_ray<'a>(&'a mut self, pos: (i64, i64), dir: FromDirection) -> VisitState {
let mut state = self.empty_state();
self.cast_ray_inner(&mut state, pos, dir);
state
fn cast_ray(&self, pos: (i64, i64), dir: FromDirection) -> VisitState {
self.cast_ray_inner(self.empty_state(), pos, dir)
}
fn cast_ray_inner<'a>(
&'a mut self,
state: &'a mut VisitState,
fn cast_ray_inner(
&self,
mut state: VisitState,
pos: (i64, i64),
dir: FromDirection,
) {
) -> VisitState {
if pos.0 >= 0
&& pos.1 >= 0
&& pos.0 < self.width()
@ -169,11 +167,14 @@ impl Contraption {
{
match dir.interact(self.tiles[pos.1 as usize][pos.0 as usize]) {
Interaction::One(dir) => self.cast_ray_inner(state, dir.goes_pos(pos), dir),
Interaction::Two((dir1, dir2)) => {
self.cast_ray_inner(state, dir1.goes_pos(pos), dir1);
self.cast_ray_inner(state, dir2.goes_pos(pos), dir2);
Interaction::Two((dir1, dir2)) => self.cast_ray_inner(
self.cast_ray_inner(state, dir2.goes_pos(pos), dir2),
dir1.goes_pos(pos),
dir1,
),
}
};
} else {
state
}
}
fn empty_state(&self) -> VisitState {
@ -198,14 +199,14 @@ impl<T: BufRead> From<Lines<T>> for Contraption {
// PROBLEM 1 solution
fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
let mut contraption = Contraption::from(input);
let contraption = Contraption::from(input);
contraption.cast_ray((0, 0), FromDirection::Left).score()
}
// PROBLEM 2 solution
fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
let mut contraption = Contraption::from(input);
let contraption = Contraption::from(input);
let rows_max = (0..contraption.height()).fold(0, |max_tiles, y| {
std::cmp::max(