Enum advent_of_code_2021::day_18::SnailfishNumber

enum SnailfishNumber {
    Num(u8),
    Pair(Box<SnailfishNumber>, Box<SnailfishNumber>),
}

Represents a snailfish number as a binary tree

Variants

Num(u8)

Tuple Fields

0: u8

Leaf node

Pair(Box<SnailfishNumber>, Box<SnailfishNumber>)

Tuple Fields

0: Box<SnailfishNumber>

1: Box<SnailfishNumber>

Branch node - branches need to be boxed so that it has a constant size

Implementations

impl SnailfishNumber

fn add(&self, other: &SnailfishNumber) -> SnailfishNumber

Combine the two halves into a new SnailfishNumber::Pair, then repeatedly call SnailfishNumber::check_depth, and SnailfishNumber::check_digits until neither change the tree.

fn with(&mut self, dir: Direction, num: u8)

Utility used by SnailfishNumber::check_depth to add one half of a pair to the next digit on the same side of the tree. dir indicates which way this number is travelling, and num is the actual digit to be added.

fn num(&self) -> u8

Helper for extracting the value when you know you’re at a leaf node.

fn check_depth(&mut self, depth: u8) -> Option<(u8, u8)>

Recursively walk the tree, if a Pair is found that is too deep, replace it with a leaf node with value 0, then pass the two halves of the pair back up so that they can be added to the next leftmost and rightmost leaves. As this is unwinding, assign the relevant side of the returned digit pair to the other half before passing the rest back up. See also SnailfishNumber::with that helps with resolving the explosion.

fn check_digits(&mut self) -> bool

Recursively hunt for a leaf that is >9, i.e. not a digit, and of one is found split it into a pair, each leaf of which is half the original (rounding halves down and up respectively so that they sum to the original). Returns true if an oversize leaf was found and split, false otherwise.

fn magnitude(&self) -> usize

Recursively combine pairs into a single number using the formula lhs x 3 + rhs x 2.

Trait Implementations

impl Clone for SnailfishNumber

fn clone(&self) -> SnailfishNumber

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for SnailfishNumber

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'a> From<&'a str> for SnailfishNumber

fn from(s: &str) -> Self

Parse a line of the input as a SnailfishNumber

impl PartialEq<SnailfishNumber> for SnailfishNumber

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

This method tests for self and other values to be equal, and is used by ==.

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

This method tests for !=.

impl Eq for SnailfishNumber

impl StructuralEq for SnailfishNumber

impl StructuralPartialEq for SnailfishNumber