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use cached::cached;
use rpds::rbt_set;
use rpds::vector::Vector;
use rpds::RedBlackTreeMap;
use rpds::RedBlackTreeMapSync;
use std::fmt;
use std::io;
use std::io::prelude::*;
use std::iter;
use std::iter::FromIterator;
use std::process;
use std::str::FromStr;
use structopt::StructOpt;
#[derive(Debug, StructOpt)]
#[structopt(name = "Day 22: Slam Shuffle")]
/// Shuffles some cards.
///
/// See https://adventofcode.com/2019/day/22 for details.
struct Opt {
/// The size of the deck
deck_size: usize,
/// At the end, query the position of card
card: usize,
}
fn main() {
let stdin = io::stdin();
let opt = Opt::from_args();
let instructions = stdin
.lock()
.lines()
.map(|x| exit_on_failed_assertion(x, "Error reading input"))
.map(|x| exit_on_failed_assertion(x.parse::<Instruction>(), "Parse error"))
.collect::<Vec<Instruction>>();
//eprintln!("{:?}", instructions);
println!(
"{}",
Deck::new(opt.deck_size)
.shuffle(&instructions)
.find_position(opt.card)
);
}
fn exit_on_failed_assertion<A, E: std::error::Error>(data: Result<A, E>, message: &str) -> A {
match data {
Ok(data) => data,
Err(e) => {
eprintln!("{}: {}", message, e);
process::exit(1);
}
}
}
#[derive(Clone)]
struct Deck {
zero: usize,
cards: Vector<usize>,
}
impl Deck {
fn new(deck_size: usize) -> Self {
Deck {
zero: 0,
cards: (0..deck_size).collect(),
}
}
fn shuffle(&self, instructions: &[Instruction]) -> Deck {
instructions.iter().fold(self.clone(), |deck, instruction| {
//eprintln!("{} :: {}", deck.zero, deck.cards);
deck.single_shuffle(instruction)
})
}
fn single_shuffle(&self, instruction: &Instruction) -> Deck {
match instruction {
Instruction::DealIntoNewStack => Deck {
cards: (0..self.cards.len())
.map(|i| self.at(self.cards.len() - i - 1))
.collect(),
zero: 0,
},
Instruction::Cut(n) => Deck {
zero: mod_plus(self.zero, *n, self.cards.len()),
..self.clone()
},
Instruction::ReverseCut(n) => Deck {
zero: mod_sub(self.zero, *n, self.cards.len()),
..self.clone()
},
Instruction::DealWithIncrement(n) => Deck {
cards: (0..self.cards.len())
.map(|i| self.at(*layout_after_shift(*n, self.cards.len()).get(&i).unwrap()))
.collect(),
zero: 0,
},
}
}
fn at(&self, index: usize) -> usize {
self.cards[mod_plus(index, self.zero, self.cards.len())]
}
fn find_position(&self, value: usize) -> usize {
mod_sub(
self.cards.iter().position(|x| *x == value).unwrap(),
self.zero,
self.cards.len(),
)
}
}
fn mod_plus(a: usize, b: usize, modulus: usize) -> usize {
(a + b) % modulus
}
fn mod_sub(a: usize, b: usize, modulus: usize) -> usize {
(a + modulus - b) % modulus
}
fn mod_times(a: usize, b: usize, modulus: usize) -> usize {
(a * b) % modulus
}
cached! {
LAYOUT_AFTER_SHIFT;
fn layout_after_shift(n: usize, modulus: usize) -> RedBlackTreeMapSync<usize, usize> = {
(0..modulus).fold(RedBlackTreeMapSync::new_sync(), |acc, next| {
acc.insert(mod_times(next, n, modulus), next)
})
}
}
#[derive(Debug)]
enum Instruction {
DealIntoNewStack,
Cut(usize),
ReverseCut(usize),
DealWithIncrement(usize),
}
impl FromStr for Instruction {
type Err = ParseErr;
fn from_str(s: &str) -> Result<Self, Self::Err> {
if s.starts_with("deal into new stack") {
Ok(Instruction::DealIntoNewStack)
} else if s.starts_with("cut -") {
s.split(' ')
.nth(1)
.map(|val| {
val.parse::<isize>()
.map_err(|_| ParseErr)
.map(|parsed| Instruction::ReverseCut(parsed.abs() as usize))
})
.unwrap_or(Err(ParseErr))
} else if s.starts_with("cut") {
s.split(' ')
.nth(1)
.map(|val| {
val.parse::<usize>()
.map_err(|_| ParseErr)
.map(|parsed| Instruction::Cut(parsed))
})
.unwrap_or(Err(ParseErr))
} else if s.starts_with("deal with increment") {
s.split(' ')
.nth(3)
.map(|val| {
val.parse::<usize>()
.map_err(|_| ParseErr)
.map(|parsed| Instruction::DealWithIncrement(parsed))
})
.unwrap_or(Err(ParseErr))
} else {
Err(ParseErr)
}
}
}
#[derive(Debug, Clone, Copy)]
struct ParseErr;
impl fmt::Display for ParseErr {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Error parsing input")
}
}
impl std::error::Error for ParseErr {}
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