Struct aoc::year2021::day23::Room

struct Room {
    packed: u16,
}

Pack the room state into only 2 bytes.

We use 3 bits for each amphipod plus a marker bit for a maximum of 13 bits. The room is a stack with the amphipod closest to the hallway in the least significant position.

The marker bit is used to determine how full a room is and to disambiguate empty from the A type.

Some example rooms:

• Empty room 0000000000000001
• Room with two As 0000000001000000
• Room with ABCD where A is closest to hallway 0001011010001000

Fields

packed: u16

Implementations

impl Room

fn new(spaces: [usize; 4]) -> Room

Pack state into a compact u16 representation.

fn size(self) -> usize

The marker bit is always in the most significant position, so can be used to find out the size of a room.

fn peek(self) -> Option<usize>

Find the type of an amphipod closest to the hallway.

fn pop(&mut self) -> usize

Remove the top amphipod.

fn open(self, kind: usize) -> bool

A room is “open” if amphipods of that type can move to it. This means that it must be empty or only already contain amphipods of that type.

We use a multiplication by a constant to figure out the bit pattern. For example a room with three Bs would have a bit pattern of 0000001001001001 which is the marker bit plus B << 6 + B << 3 + B << 0 = B * 64 + B * 8 + B = B * 73.

fn push(&mut self, kind: usize)

Return an amphipod to the correct room.

fn spaces(self, index: usize) -> usize

Returns the amphipod at a specific index from the bottom of the burrow. 0 is the bottom amphipod furthest from the hallway, 1 the next closest and so on.

Trait Implementations

impl Clone for Room

fn clone(&self) -> Room

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Hash for Room

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Room

fn eq(&self, other: &Room) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Room

impl Eq for Room

impl StructuralPartialEq for Room