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day21.rs
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day21.rs
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//! [Day 21: Monkey Math](https://adventofcode.com/2022/day/21)
use num::Rational64;
use std::collections::HashMap;
use std::ops;
enum Job {
Number(i64),
Operation((String, char, String)),
}
/// Store an affine equation ax+b
#[derive(Debug)]
struct Affine {
a: Rational64,
b: Rational64,
}
struct Puzzle {
monkeys: HashMap<String, Job>,
}
impl Puzzle {
fn new() -> Self {
Self {
monkeys: HashMap::new(),
}
}
/// Loads data from input (one line)
fn configure(&mut self, path: &str) {
let data = std::fs::read_to_string(path).unwrap();
for line in data.lines() {
if line.is_empty() {
continue;
}
let mut it = line.split(':');
let monkey = it.next().unwrap();
let job = it.next().unwrap().trim();
// println!("job {}={}", monkey, job);
if let Ok(n) = job.parse::<i64>() {
self.monkeys.insert(monkey.to_string(), Job::Number(n));
} else {
let mut args = job.split(' ');
let l = args.next().unwrap().to_string();
let o = args.next().unwrap().chars().next().unwrap();
let r = args.next().unwrap().to_string();
self.monkeys
.insert(monkey.to_string(), Job::Operation((l, o, r)));
}
}
}
fn eval(&self, var: &str) -> i64 {
if let Some(m) = self.monkeys.get(var) {
match m {
Job::Number(n) => *n,
Job::Operation((l, o, r)) => {
let l = self.eval(l);
let r = self.eval(r);
match o {
'+' => l + r,
'-' => l - r,
'*' => l * r,
'/' => l / r,
_ => panic!("unknown operation"),
}
}
}
} else {
panic!("???");
}
}
fn eval_sym(&self, var: &str) -> Affine {
if var == "humn" {
Affine::from_x()
} else if let Some(m) = self.monkeys.get(var) {
match m {
Job::Number(n) => Affine::from(*n),
Job::Operation((l, o, r)) => {
let l = self.eval_sym(l);
let r = self.eval_sym(r);
return match o {
'+' => l + r,
'-' => l - r,
'*' => l * r,
'/' => l / r,
_ => panic!("unknown operation"),
};
}
}
} else {
panic!("???");
}
}
// Solves part one
fn part1(&self) -> i64 {
self.eval("root")
}
// Solve part two
fn part2(&self) -> i64 {
let eq = match self.monkeys.get("root") {
Some(Job::Operation((l, _, r))) => self.eval_sym(l) - self.eval_sym(r),
_ => panic!("root problem"),
};
let x = eq.x();
// we expect an integer solution
assert_eq!(x.denom(), &1);
*x.numer()
}
}
/// main function
fn main() {
let args = aoc::parse_args();
let mut puzzle = Puzzle::new();
puzzle.configure(&args.path);
println!("{}", puzzle.part1());
println!("{}", puzzle.part2());
}
#[test]
fn test01() {
let mut puzzle = Puzzle::new();
puzzle.configure("test.txt");
assert_eq!(puzzle.part1(), 152);
assert_eq!(puzzle.part2(), 301);
}
impl Affine {
fn from(n: i64) -> Self {
Affine {
a: Rational64::from_integer(0),
b: Rational64::from_integer(n),
}
}
fn from_x() -> Self {
Affine {
a: Rational64::from_integer(1),
b: Rational64::from_integer(0),
}
}
fn x(&self) -> Rational64 {
-self.b / self.a
}
}
impl ops::Add<Affine> for Affine {
type Output = Affine;
fn add(self, _rhs: Affine) -> Affine {
Affine {
a: self.a + _rhs.a,
b: self.b + _rhs.b,
}
}
}
impl ops::Sub<Affine> for Affine {
type Output = Affine;
fn sub(self, _rhs: Affine) -> Affine {
Affine {
a: self.a - _rhs.a,
b: self.b - _rhs.b,
}
}
}
impl ops::Mul<Affine> for Affine {
type Output = Affine;
fn mul(self, _rhs: Affine) -> Affine {
if self.a.numer() == &0 {
Affine {
a: self.b * _rhs.a,
b: self.b * _rhs.b,
}
} else if _rhs.a.numer() == &0 {
Affine {
a: self.a * _rhs.b,
b: self.b * _rhs.b,
}
} else {
// cannot (ax+b)*(cx+d)
panic!("mul");
}
}
}
impl ops::Div<Affine> for Affine {
type Output = Affine;
fn div(self, _rhs: Affine) -> Affine {
// cannot A/(ax+b)
assert_eq!(_rhs.a.numer(), &0);
Affine {
a: self.a / _rhs.b,
b: self.b / _rhs.b,
}
}
}
impl std::fmt::Display for Affine {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "{}x + {}", self.a, self.b)
}
}