2020: day12: impl direction rotation in direction
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@ -51,6 +51,46 @@ enum Direction {
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West,
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}
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impl Direction {
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const CLOCKWISE_DIRECTIONS: &'static [Direction] = &[
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Direction::North,
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Direction::East,
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Direction::South,
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Direction::West,
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];
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fn rotate(self, turn_dir: TurnDirection, degrees: u16) -> Direction {
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debug_assert!(degrees % 90 == 0, "only right angles are supported");
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let quadrants = (degrees / 90) as usize;
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let directions_iter = Self::CLOCKWISE_DIRECTIONS.iter().copied();
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if turn_dir == TurnDirection::Left {
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// go through cardinal directions the other way around, anti-clockwise
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Self::find_direction(directions_iter.rev(), quadrants, self)
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} else {
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Self::find_direction(directions_iter, quadrants, self)
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}
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}
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fn find_direction<I>(iter: I, quarters: usize, current_direction: Direction) -> Direction
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where
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I: Iterator<Item = Direction>,
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I: std::clone::Clone,
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{
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iter
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// this is litteraly a circle, reaching West and turning 90 degrees right means facing
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// North again
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.cycle()
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// find our current ship direction
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.skip_while(|dir| *dir != current_direction)
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// skip as many quarters as needed
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.nth(quarters)
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// we can unwrap safely because we called .cycle() on a non empty iterator
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.unwrap()
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}
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}
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum TurnDirection {
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Left,
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@ -127,53 +167,16 @@ impl Ship {
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}
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}
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const CLOCKWISE_DIRECTIONS: &'static [Direction] = &[
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Direction::North,
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Direction::East,
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Direction::South,
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Direction::West,
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];
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fn manhattan_distance(&self) -> i64 {
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self.x.abs() + self.y.abs()
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}
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fn find_direction<I>(iter: I, quarters: usize, current_direction: Direction) -> Direction
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where
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I: Iterator<Item = Direction>,
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I: std::clone::Clone,
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{
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iter
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// this is litteraly a circle, reaching West and turning 90 degrees right means
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// facing North again
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.cycle()
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// find our current ship direction
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.skip_while(|dir| *dir != current_direction)
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// skip as many quarters as needed
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.nth(quarters)
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// we can unwrap safely because we called .cycle() on a non empty iterator
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.unwrap()
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}
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fn process(&mut self, action: Action) {
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match action.kind {
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ActionKind::Move(dir) => self.forward(dir, action.arg),
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ActionKind::Turn(turn_dir) => {
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debug_assert!(action.arg % 90 == 0, "only right angles are supported");
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let quarters = (action.arg / 90) as usize;
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let directions_iter = Self::CLOCKWISE_DIRECTIONS.iter().copied();
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let new_dir = if turn_dir == TurnDirection::Left {
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// go through cardinal directions the other way around, anti-clockwise
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Ship::find_direction(directions_iter.rev(), quarters, self.direction)
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} else {
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Ship::find_direction(directions_iter, quarters, self.direction)
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};
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self.direction = new_dir;
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self.direction = self.direction.rotate(turn_dir, action.arg);
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}
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ActionKind::Forward => self.forward(self.direction, action.arg),
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