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|
use nom::{
branch::alt,
character::complete::{char as nom_char, line_ending, u8 as nom_u8},
combinator::map,
multi::separated_list1,
sequence::tuple,
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_18.txt")?;
let snail_nums = parse_snail_nums(&input).unwrap().1;
{
let mut snail_nums_iter = snail_nums.clone().into_iter();
let sum = snail_nums_iter
.next()
.map(|first_num| snail_nums_iter.fold(first_num, |acc, next| acc + next))
.expect("Expected at least one snail number");
dbg!(&sum);
dbg!(sum.magnitude());
}
let mut max_magnitude = 0;
for i in 0..snail_nums.len() {
for j in 0..snail_nums.len() {
if i != j {
let new_magnitude = (snail_nums[i].clone() + snail_nums[j].clone()).magnitude();
if new_magnitude > max_magnitude {
max_magnitude = new_magnitude;
}
}
}
}
dbg!(max_magnitude);
Ok(())
}
#[derive(Debug, Clone, PartialEq, Eq)]
enum SnailNum {
Regular(u8),
Pair(Box<SnailNum>, Box<SnailNum>),
}
impl Default for SnailNum {
fn default() -> SnailNum {
SnailNum::Regular(0)
}
}
#[derive(PartialEq, Eq)]
enum NormalizeResult {
AlreadyNormalized,
NormalizeActionHandledInternally,
Explode(u8, u8),
}
impl SnailNum {
fn unwrap_val(&self) -> u8 {
match self {
SnailNum::Regular(val) => *val,
SnailNum::Pair(_, _) => panic!("unwrapped the val on a pair"),
}
}
fn add_to_left(&mut self, add: u8) {
match self {
Self::Regular(val) => *val += add,
Self::Pair(left, _) => left.add_to_left(add),
}
}
fn add_to_right(&mut self, add: u8) {
match self {
Self::Regular(val) => *val += add,
Self::Pair(_, right) => right.add_to_right(add),
}
}
fn normalize_split_pass(&mut self) -> NormalizeResult {
match self {
Self::Regular(val) => {
if *val > 9 {
let half = *val / 2;
*self = SnailNum::Pair(
Box::new(SnailNum::Regular(half)),
Box::new(SnailNum::Regular(if *val % 2 == 0 {
half
} else {
half + 1
})),
);
return NormalizeResult::NormalizeActionHandledInternally;
}
}
Self::Pair(left, right) => {
match left.normalize_split_pass() {
NormalizeResult::AlreadyNormalized => {}
_ => {
return NormalizeResult::NormalizeActionHandledInternally;
}
}
match right.normalize_split_pass() {
NormalizeResult::AlreadyNormalized => {}
_ => {
return NormalizeResult::NormalizeActionHandledInternally;
}
}
}
}
NormalizeResult::AlreadyNormalized
}
fn normalize_explode_pass(&mut self, current_depth: u8) -> NormalizeResult {
match self {
Self::Regular(_val) => {}
Self::Pair(left, right) => {
if current_depth >= 4 {
let result = NormalizeResult::Explode(left.unwrap_val(), right.unwrap_val());
*self = SnailNum::Regular(0);
return result;
}
match left.normalize_explode_pass(current_depth + 1) {
NormalizeResult::AlreadyNormalized => {}
NormalizeResult::NormalizeActionHandledInternally => {
return NormalizeResult::NormalizeActionHandledInternally;
}
NormalizeResult::Explode(leftadd, rightadd) => {
right.add_to_left(rightadd);
return NormalizeResult::Explode(leftadd, 0);
}
}
match right.normalize_explode_pass(current_depth + 1) {
NormalizeResult::AlreadyNormalized => {}
NormalizeResult::NormalizeActionHandledInternally => {
return NormalizeResult::NormalizeActionHandledInternally;
}
NormalizeResult::Explode(leftadd, rightadd) => {
left.add_to_right(leftadd);
return NormalizeResult::Explode(0, rightadd);
}
}
}
}
NormalizeResult::AlreadyNormalized
}
fn normalize(&mut self) {
let mut normalized = false;
while !normalized {
let explode_result = self.normalize_explode_pass(0);
if explode_result == NormalizeResult::AlreadyNormalized {
let split_result = self.normalize_split_pass();
if split_result == NormalizeResult::AlreadyNormalized {
normalized = true;
}
}
}
}
fn magnitude(&self) -> u64 {
match self {
Self::Regular(val) => *val as u64,
Self::Pair(left, right) => 3 * left.magnitude() + 2 * right.magnitude(),
}
}
}
impl std::ops::Add<SnailNum> for SnailNum {
type Output = SnailNum;
fn add(self, other: SnailNum) -> SnailNum {
let mut result = SnailNum::Pair(Box::new(self), Box::new(other));
result.normalize();
result
}
}
fn parse_snail_nums(input: &str) -> IResult<&str, Vec<SnailNum>> {
separated_list1(line_ending, parse_snail_num)(input)
}
fn parse_snail_num(input: &str) -> IResult<&str, SnailNum> {
alt((
map(nom_u8, SnailNum::Regular),
map(
tuple((
nom_char('['),
parse_snail_num,
nom_char(','),
parse_snail_num,
nom_char(']'),
)),
|(_, left, _, right, _)| SnailNum::Pair(Box::new(left), Box::new(right)),
),
))(input)
}
|
