2020: day23: part 1

This commit is contained in:
Antoine Martin 2020-12-23 23:58:34 +01:00
parent 002f1a2b04
commit 9888140072
6 changed files with 163 additions and 0 deletions

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@ -21,6 +21,7 @@ use aoc2020::day18;
use aoc2020::day19; use aoc2020::day19;
use aoc2020::day21; use aoc2020::day21;
use aoc2020::day22; use aoc2020::day22;
use aoc2020::day23;
fn aoc2020_all(c: &mut Criterion) { fn aoc2020_all(c: &mut Criterion) {
c.bench_function("day01", |b| b.iter(|| day01::run().unwrap())); c.bench_function("day01", |b| b.iter(|| day01::run().unwrap()));
@ -44,6 +45,7 @@ fn aoc2020_all(c: &mut Criterion) {
c.bench_function("day19", |b| b.iter(|| day19::run().unwrap())); c.bench_function("day19", |b| b.iter(|| day19::run().unwrap()));
c.bench_function("day21", |b| b.iter(|| day21::run().unwrap())); c.bench_function("day21", |b| b.iter(|| day21::run().unwrap()));
c.bench_function("day22", |b| b.iter(|| day22::run().unwrap())); c.bench_function("day22", |b| b.iter(|| day22::run().unwrap()));
c.bench_function("day23", |b| b.iter(|| day23::run().unwrap()));
} }
criterion_group! { criterion_group! {

1
aoc2020/input/day23.txt Normal file
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@ -0,0 +1 @@
315679824

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@ -0,0 +1 @@
389125467

156
aoc2020/src/day23.rs Normal file
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@ -0,0 +1,156 @@
use std::{collections::VecDeque, fmt::Write};
use anyhow::{Context, Result};
const INPUT: &str = include_str!("../input/day23.txt");
pub fn run() -> Result<String> {
let mut res = String::with_capacity(128);
writeln!(res, "part 1: {}", part1(INPUT)?)?;
Ok(res)
}
fn part1(input: &str) -> Result<String> {
let mut cup_circle: CupCircle = input.parse()?;
for _ in 0..100 {
cup_circle.step();
}
Ok(format!("{}", cup_circle))
}
struct CupCircle(VecDeque<u64>);
/// CupCircle provides an abstraction over a VecDeque to emulate the steps of the game
///
/// The "current" cup should always be the first one in the VecDeque at the end of a turn, for
/// convenience
///
/// The Circle should never become empty if you only use its public interface, so all calls to
/// unwrap() in its implementation should never panic.
impl CupCircle {
pub fn front(&self) -> u64 {
*self.0.front().unwrap()
}
fn pop_front(&mut self) -> u64 {
self.0.pop_front().unwrap()
}
fn push_back(&mut self, value: u64) {
self.0.push_back(value);
}
pub fn max(&self) -> u64 {
*self.0.iter().max().unwrap()
}
fn remove_next_3(&mut self) -> [u64; 3] {
let first = self.pop_front();
let second = self.pop_front();
let third = self.pop_front();
[first, second, third]
}
/// Shifts the cup circle, putting the first cup at the end of the deque
///
/// This doesn't change anything to the cup circle layout, except that the new first cup is
/// considered the "current" cup at the end of a step in our implementation
fn shift(&mut self) {
let front = self.0.pop_front().unwrap();
self.0.push_back(front);
}
/// Executes one step of the game
pub fn step(&mut self) {
let current = self.front();
// skip current
self.shift();
// The crab picks up the three cups that are immediately clockwise of the current cup. They
// are removed from the circle; cup spacing is adjusted as necessary to maintain the circle.
let removed_cups = self.remove_next_3();
// The crab selects a destination cup: the cup with a label equal to the current cup's label
// minus one. If this would select one of the cups that was just picked up, the crab will
// keep subtracting one until it finds a cup that wasn't just picked up. If at any point in
// this process the value goes below the lowest value on any cup's label, it wraps around to
// the highest value on any cup's label instead.
//
// TODO: use std::cmp::Ord::clamp when stabilized (Rust 1.50)
let mut destination = if current > 1 { current - 1 } else { self.max() };
while removed_cups.contains(&destination) {
destination = if destination > 1 {
destination - 1
} else {
self.max()
};
}
// place destination in front
while self.front() != destination {
self.shift();
}
// The crab places the cups it just picked up so that they are immediately clockwise of the
// destination cup. They keep the same order as when they were picked up.
//
// For this, let's put the destination at the end of the queue by shifting one last time
self.shift();
removed_cups.iter().for_each(|cup| self.push_back(*cup));
// The crab selects a new current cup: the cup which is immediately clockwise of the current
// cup.
while self.front() != current {
self.shift();
}
self.shift();
}
}
impl std::str::FromStr for CupCircle {
type Err = anyhow::Error;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let circle = s
.trim_end()
.chars()
.map(|c| Ok(c.to_digit(10).context("character was not a digit")? as u64))
.collect::<Result<_>>()?;
Ok(CupCircle(circle))
}
}
impl std::fmt::Display for CupCircle {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.0
.iter()
.cycle()
.skip_while(|cup| **cup != 1)
.skip(1)
.take(8)
.try_for_each(|cup| write!(f, "{}", cup))
}
}
#[cfg(test)]
mod tests {
use super::*;
const PROVIDED: &str = include_str!("../input/day23_provided.txt");
#[test]
fn part1_provided() {
assert_eq!(part1(PROVIDED).unwrap(), "67384529");
}
#[test]
fn part1_real() {
assert_eq!(part1(INPUT).unwrap(), "72496583");
}
}

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@ -21,3 +21,4 @@ pub mod day18;
pub mod day19; pub mod day19;
pub mod day21; pub mod day21;
pub mod day22; pub mod day22;
pub mod day23;

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@ -23,6 +23,7 @@ use aoc2020::day18;
use aoc2020::day19; use aoc2020::day19;
use aoc2020::day21; use aoc2020::day21;
use aoc2020::day22; use aoc2020::day22;
use aoc2020::day23;
fn main() -> Result<()> { fn main() -> Result<()> {
let days: &[DayFunc] = &[ let days: &[DayFunc] = &[
@ -47,6 +48,7 @@ fn main() -> Result<()> {
day19::run, day19::run,
day21::run, day21::run,
day22::run, day22::run,
day23::run,
]; ];
aoc::run(days) aoc::run(days)