contests/advent_of_code/2022/11/src/main.rs

use std::collections::VecDeque;

use nom::{
    character::complete::{self, multispace1, one_of, multispace0},
    multi::{separated_list1, many1},
    bytes::complete::tag,
    sequence::{delimited, preceded},
    branch::alt,
    *,
};

#[derive(Debug)]
enum Value {
    Old,
    Val(u64),
} use Value::*;

#[derive(Debug)]
enum Operation {
    Mult(Value),
    Add(Value),
} use Operation::*;

#[derive(Debug)]
pub struct Test {
    divisible_by: u64,
    on_false: usize,
    on_true: usize,
}

#[derive(Debug)]
pub struct Monkey {
    items: VecDeque<u64>,
    operation: Operation,
    test: Test,
    number_of_inspections: u64,
}

impl Monkey {
    pub fn handle_items(&mut self, magic_number: u64) -> Vec<(u64, usize)> {
        let mut result = Vec::new();
        
        while !self.items.is_empty() {
            self.number_of_inspections += 1;

            let mut item = self.items.pop_front().unwrap();
            item = match self.operation {
                Mult(Old) => {item * item},
                Mult(Val(num)) => {item * num},
                Add(Old) => {item * 2},
                Add(Val(num)) => {item + num},
            };

            // item /= 3;
            item = item % magic_number;

            let throw_to_monkey = match item % self.test.divisible_by == 0 {
                true => self.test.on_true,
                false => self.test.on_false,
            };

            result.push((item, throw_to_monkey));
        }

        result
    }
}

fn parse_operation(input: &str) -> IResult<&str, Operation> {
    let (input, op) = preceded(
        tag("Operation: new = old "), 
        one_of("+*"),
    )(input)?;

    let (input, num) : (&str, Value) = preceded(        
        multispace1, 
        alt((
            complete::u64.map(|num| Value::Val(num)),
            tag("old").map(|_| Value::Old),
        )),
    )(input)?;

    let func = match op {
        '*' => Operation::Mult(num),
        '+' => Operation::Add(num),
        _ => unreachable!(),
    };

    Ok((input, func))
}

fn parse_test(input: &str) -> IResult<&str, Test> {
    let (input, divisible_by) = preceded(
        tag("Test: divisible by "),
        complete::u64,
    )(input)?;

    let (input, _) = multispace1(input)?;

    let (input, on_true) = preceded(
        tag("If true: throw to monkey "), 
        complete::u32,
    )(input)?;

    let (input, _) = multispace1(input)?;

    let (input, on_false) = preceded(
        tag("If false: throw to monkey "), 
        complete::u32,
    )(input)?;

    // Generate Test

    let t = Test {
        divisible_by,
        on_false: on_false as usize,
        on_true: on_true as usize,
    };

    Ok((input, t))
}

fn parse_input(input: &str) -> IResult<&str, Monkey> {
    // Parse: Monkey _id:
    let (input, _id) = delimited(
        tag("Monkey "), 
        complete::u32, 
        tag(":"),
    )(input)?;

    let (input, _) = multispace1(input)?;

    // Parse: Starting items: num1, num2
    let (input, levels) = preceded(
        tag("Starting items: "), 
        separated_list1(tag(", "), complete::u64),
    )(input)?;

    let (input, _) = multispace1(input)?;

    //Parse: Operation: new = old {+ num|old}, {* num|old}
    let (input, operation) = parse_operation(input)?;

    let (input, _) = multispace1(input)?;

    //Parse: Test: divisible by num
    //         If true: throw to monkey #
    //         If false: throw to monkey #
    let (input, test) = parse_test(input)?;
    
    let (input, _) = multispace0(input)?;

    // Generate a monkey here

    let items = VecDeque::from_iter(levels);

    let m = Monkey {
        items,
        operation,
        test,
        number_of_inspections: 0,
    };

    Ok((input, m))
}

fn part1and2() {
    let input_text = include_str!("../input.txt");
    let (_, mut monkeys) = many1(parse_input)(input_text).unwrap();

    let magic_number = monkeys
        .iter()
        .map(|m| m.test.divisible_by)
        .product();

    for _i in 0..10000 {
        for monkey_index in 0..monkeys.len() {
            let monkey = monkeys.get_mut(monkey_index).unwrap();
            let new_item_list = monkey.handle_items(magic_number);

            for (item, thrown_to_monkey) in new_item_list {
                monkeys[thrown_to_monkey].items.push_back(item);
            }
        }
    }

    let mut results = monkeys
        .iter()
        .map(|m| m.number_of_inspections)
        .collect::<Vec<u64>>();
    results.sort_by(|a, b| b.cmp(a));

    println!("{} * {} =  {}", results[0], results[1], results[0] * results[1]);

}

fn main() {
    part1and2();
}