196 lines
4.9 KiB
Rust
196 lines
4.9 KiB
Rust
#![warn(clippy::pedantic)]
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use std::{
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cmp::Reverse,
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io::{stdin, Read},
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ops::Rem,
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str::FromStr,
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};
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum Operand {
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Const(usize),
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Old,
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}
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impl Operand {
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fn evaluate(self, old: usize) -> usize {
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match self {
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Self::Old => old,
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Self::Const(c) => c,
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}
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}
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}
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impl FromStr for Operand {
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type Err = std::num::ParseIntError;
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fn from_str(s: &str) -> Result<Self, Self::Err> {
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match s {
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"old" => Ok(Operand::Old),
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i => i.parse().map(Operand::Const),
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}
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}
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}
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum Operation {
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Add(Operand),
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Multiply(Operand),
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Divide(Operand),
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}
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum Test {
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Divisible(usize),
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}
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#[derive(Debug, Clone, PartialEq, Eq)]
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struct Item {
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value: usize,
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}
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impl Item {
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fn apply_operation(&mut self, op: Operation, modulo: Option<usize>) {
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match op {
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Operation::Add(x) => self.value += x.evaluate(self.value),
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Operation::Multiply(x) => self.value *= x.evaluate(self.value),
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Operation::Divide(x) => {
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assert!(modulo.is_none(), "can't divide under modulo arithmetic");
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self.value /= x.evaluate(self.value);
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}
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}
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if let Some(modulo) = modulo {
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self.value %= modulo;
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}
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}
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fn apply_test(&self, test: Test) -> bool {
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match test {
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Test::Divisible(n) => self.value.rem(n) == 0,
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}
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}
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}
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#[derive(Debug, Clone, PartialEq, Eq)]
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struct Monkey {
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items: Vec<Item>,
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operation: Operation,
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test: Test,
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target_pass: usize,
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target_fail: usize,
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inspections: usize,
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}
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impl Monkey {
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fn throw_item(&mut self, divisor: Option<usize>, modulo: Option<usize>) -> (usize, Item) {
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self.inspections += 1;
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let mut item = self.items.remove(0);
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item.apply_operation(self.operation, modulo);
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if let Some(divisor) = divisor {
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item.apply_operation(Operation::Divide(Operand::Const(divisor)), modulo);
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}
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let target = if item.apply_test(self.test) {
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self.target_pass
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} else {
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self.target_fail
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};
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(target, item)
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}
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}
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impl FromStr for Monkey {
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type Err = ();
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fn from_str(s: &str) -> Result<Self, Self::Err> {
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let mut lines = s.lines();
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lines.next().ok_or(())?; // Monkey n:
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let mut with_prefix = |prefix: &str| lines.next().ok_or(())?.strip_prefix(prefix).ok_or(());
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let items: Vec<_> = with_prefix(" Starting items: ")?
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.split(", ")
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.map(|i| {
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let value = i.parse().map_err(drop)?;
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Ok(Item { value })
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})
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.collect::<Result<_, _>>()?;
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let (operator, operand) = with_prefix(" Operation: new = old ")?
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.split_once(' ')
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.ok_or(())?;
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let operand = operand.parse().map_err(drop)?;
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let operation = match operator {
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"+" => Operation::Add(operand),
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"*" => Operation::Multiply(operand),
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_ => panic!("invalid operator {operator}"),
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};
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let test = Test::Divisible(
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with_prefix(" Test: divisible by ")?
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.parse()
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.map_err(drop)?,
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);
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let target_pass = with_prefix(" If true: throw to monkey ")?
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.parse()
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.map_err(drop)?;
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let target_fail = with_prefix(" If false: throw to monkey ")?
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.parse()
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.map_err(drop)?;
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Ok(Monkey {
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items,
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operation,
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test,
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target_pass,
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target_fail,
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inspections: 0,
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})
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}
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}
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fn play(monkeys: &mut [Monkey], rounds: usize, divisor: Option<usize>) -> usize {
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let modulo = match divisor {
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Some(_) => None,
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None => Some(
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monkeys
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.iter()
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.map(|m| {
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let Test::Divisible(i) = m.test;
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i
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})
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.product(),
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),
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};
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for _round in 0..rounds {
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for i in 0..monkeys.len() {
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for _j in 0..monkeys[i].items.len() {
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let (target, item) = monkeys[i].throw_item(divisor, modulo);
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monkeys[target].items.push(item);
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}
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}
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}
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let mut levels: Vec<_> = monkeys.iter().map(|m| m.inspections).collect();
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levels.sort_unstable_by_key(|i| Reverse(*i));
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levels[0] * levels[1]
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}
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fn main() {
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let mut data = String::new();
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stdin().read_to_string(&mut data).unwrap();
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let mut monkeys: Vec<Monkey> = data
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.split("\n\n")
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.map(|monkey| monkey.parse().unwrap())
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.collect();
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println!("{:?}", play(&mut monkeys.clone(), 20, Some(3)));
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println!("{:?}", play(&mut monkeys, 10_000, None));
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}
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