path: root/day05b/src/main.rs

/// --- Part Two ---
///
/// As you watch the crane operator expertly rearrange the crates, you notice the process isn't
/// following your prediction.
///
/// Some mud was covering the writing on the side of the crane, and you quickly wipe it away.  The
/// crane isn't a CrateMover 9000 - it's a CrateMover 9001.
///
/// The CrateMover 9001 is notable for many new and exciting features: air conditioning, leather
/// seats, an extra cup holder, and the ability to pick up and move multiple crates at once.
///
/// Again considering the example above, the crates begin in the same configuration:
///
/// ```
///     [D]
/// [N] [C]
/// [Z] [M] [P]
///  1   2   3
/// ```
///
/// Moving a single crate from stack 2 to stack 1 behaves the same as before:
///
/// ```
/// [D]
/// [N] [C]
/// [Z] [M] [P]
///  1   2   3
/// ```
///
/// However, the action of moving three crates from stack 1 to stack 3 means that those three moved
/// crates stay in the same order, resulting in this new configuration:
///
/// ```
///         [D]
///         [N]
///     [C] [Z]
///     [M] [P]
///  1   2   3
/// ```
///
/// Next, as both crates are moved from stack 2 to stack 1, they retain their order as well:
///
/// ```
///         [D]
///         [N]
/// [C]     [Z]
/// [M]     [P]
///  1   2   3
/// ```
///
/// Finally, a single crate is still moved from stack 1 to stack 2, but now it's crate C that gets moved:
///
/// ```
///         [D]
///         [N]
///         [Z]
/// [M] [C] [P]
///  1   2   3
/// ```
///
/// In this example, the CrateMover 9001 has put the crates in a totally different order: MCD.
///
/// Before the rearrangement process finishes, update your simulation so that the Elves know where
/// they should stand to be ready to unload the final supplies.  After the rearrangement procedure
/// completes, what crate ends up on top of each stack?
use clap::Parser;
use itertools::Itertools;
use nom::branch::alt;
use nom::bytes::complete::tag;
use nom::character::complete::{alpha1, digit1, multispace1};
use nom::combinator::{map, opt, peek};
use nom::error::{ErrorKind as NomErrorKind, ParseError};
use nom::multi::{many1, many1_count};
use nom::sequence::{delimited, preceded, terminated};
use nom::IResult;

use std::fs::File;
use std::io::prelude::*;
use std::io::BufReader;
use std::iter::*;
use std::path::PathBuf;

pub type Input<'a> = &'a str;
pub type Result<'a, T> = IResult<Input<'a>, T, Error<Input<'a>>>;

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum ErrorKind {
    Nom(NomErrorKind),
    Context(&'static str),
    Custom(String),
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Error<I> {
    pub errors: Vec<(I, ErrorKind)>,
}

impl<I> ParseError<I> for Error<I> {
    fn from_error_kind(input: I, kind: NomErrorKind) -> Self {
        let errors = vec![(input, ErrorKind::Nom(kind))];
        Self { errors }
    }

    fn append(input: I, kind: NomErrorKind, mut other: Self) -> Self {
        other.errors.push((input, ErrorKind::Nom(kind)));
        other
    }
}

const FILEPATH: &'static str = "examples/input.txt";

#[derive(Parser, Debug)]
#[clap(author, version, about, long_about = None)]
struct Cli {
    #[clap(short, long, default_value = FILEPATH)]
    file: PathBuf,
}

#[derive(Debug, Clone)]
struct Supplies(Vec<Vec<char>>);

#[derive(Debug, Clone)]
struct Order {
    from: usize,
    to: usize,
    amount: usize,
}

#[derive(Debug, Clone)]
enum LineKind {
    Axis(usize),
    Crates(Vec<char>),
}

fn parse_digit(input: &str) -> Result<char> {
    map(preceded(multispace1, digit1), |s: &str| {
        s.chars().next().unwrap()
    })(input)
}

fn parse_crate(input: &str) -> Result<char> {
    map(delimited(tag("["), alpha1, tag("]")), |s: &str| {
        s.chars().next().unwrap()
    })(input)
}

fn parse_crate_or_empty(input: &str) -> Result<char> {
    terminated(alt((map(tag("   "), |_| ' '), parse_crate)), opt(tag(" ")))(input)
}

fn parse_line(input: &str) -> Result<LineKind> {
    let res = peek(parse_digit)(input);
    if res.is_ok() {
        map(many1_count(parse_digit), |len| LineKind::Axis(len))(input)
    } else {
        map(many1(parse_crate_or_empty), |v| LineKind::Crates(v))(input)
    }
}

impl Supplies {
    fn new() -> Self {
        Self(Vec::<Vec<char>>::new())
    }

    fn idx_to_internal(idx: usize) -> usize {
        idx - 1
    }

    fn initialize(&mut self, input: Vec<LineKind>) {
        let axis = &input[input.len() - 1];
        let LineKind::Axis(len) = axis else {
            panic!();
        };
        self.resize(*len);

        let _ = input
            .into_iter()
            .rev()
            .skip(1)
            .map(|x| match x {
                LineKind::Crates(v) => v,
                _ => panic!(),
            })
            .map(|vc| {
                vc.into_iter()
                    .zip(1usize..)
                    .filter(|(c, _)| *c != ' ')
                    .collect_vec()
            })
            .flatten()
            .scan(self, |state, (c, idx)| {
                state.push(idx, c);
                Some(())
            })
            .last();
    }

    fn pop(&mut self, idx: usize) -> char {
        self.0[Self::idx_to_internal(idx)].pop().unwrap()
    }

    fn peek(&self, idx: usize) -> char {
        self.0[Self::idx_to_internal(idx)][self.0[Self::idx_to_internal(idx)].len() - 1]
    }

    fn push(&mut self, idx: usize, letter: char) {
        self.0[Self::idx_to_internal(idx)].push(letter)
    }

    fn resize(&mut self, len: usize) {
        self.0.resize(len, Vec::<char>::new())
    }

    fn top_chars(&self) -> String {
        (0..self.0.len())
            .map(|idx| self.peek(idx + 1).to_string())
            .join("")
    }

    fn transfer(&mut self, order: Order) {
        let popped = (0..order.amount)
            .into_iter()
            .map(|_| self.pop(order.from))
            .collect_vec();
        for c in popped.into_iter().rev() {
            self.push(order.to, c);
        }
    }
}

fn main() {
    let args = Cli::parse();

    let file = File::open(&args.file).unwrap();
    let reader = BufReader::new(file);

    let init = reader
        .lines()
        .map(|l| l.unwrap())
        .take_while(|l| !l.is_empty())
        .map(|l| parse_line(l.as_str()).unwrap().1)
        .collect_vec();

    let mut supplies = Supplies::new();
    supplies.initialize(init);

    let file = File::open(&args.file).unwrap();
    let reader = BufReader::new(file);
    let _ = reader
        .lines()
        .map(|l| l.unwrap())
        .skip_while(|l| !l.contains("move"))
        .map(|l| {
            let sp = l.split_whitespace().collect_vec();
            Order {
                from: sp[3].parse::<usize>().unwrap(),
                to: sp[5].parse::<usize>().unwrap(),
                amount: sp[1].parse::<usize>().unwrap(),
            }
        })
        .scan(&mut supplies, |state, order| {
            state.transfer(order);
            Some(())
        })
        .last();

    println!("{}", supplies.top_chars());
}