1 files changed, 127 insertions, 0 deletions
diff --git a/2022/src/day11.rs b/2022/src/day11.rs
new file mode 100644
index 0000000..aad0b48
--- /dev/null
+++ b/2022/src/day11.rs
@@ -0,0 +1,127 @@
+mod utils;
+extern crate nom;
+use nom::{
+    branch::alt,
+    bytes::complete::{tag, take_until},
+    character::complete::{digit0, u32},
+    multi::separated_list0,
+    IResult,
+};
+use utils::{max_n, read_input};
+
+fn main() {
+    let input = read_input();
+
+    let (_, monkeys_items) = separated_list0(tag("\n\n"), Monkey::parse)(&input).unwrap();
+    let (monkeys, items): (Vec<_>, Vec<_>) = monkeys_items.into_iter().unzip();
+
+    println!(
+        "Part 1: {}",
+        monkey_business::<3, 20>(&monkeys, items.clone(), usize::MAX),
+    );
+    println!(
+        "Part 2: {}",
+        monkey_business::<1, 10000>(&monkeys, items, monkeys.iter().map(|x| x.test).product())
+    );
+}
+
+fn monkey_business<const REDUCER: usize, const ROUNDS: usize>(
+    monkeys: &[Monkey],
+    mut items: Vec<Vec<usize>>,
+    additional_reducer: usize,
+) -> usize {
+    let mut inspections = vec![0; monkeys.len()];
+    for _ in 0..ROUNDS {
+        for monkey_idx in 0..monkeys.len() {
+            let curr_monkey = &monkeys[monkey_idx];
+            while let Some(worry) = items[monkey_idx].pop() {
+                let new_worry = (curr_monkey.do_op(worry) / REDUCER) % additional_reducer;
+                inspections[monkey_idx] += 1;
+                let throw_to = curr_monkey.throw_to(new_worry);
+
+                items[throw_to].push(new_worry);
+            }
+        }
+    }
+
+    max_n(&mut inspections, 2).iter().product::<usize>()
+}
+
+#[derive(Debug)]
+struct Monkey {
+    op: Operation,
+    test: usize,
+    next_monkey: (usize, usize),
+}
+
+impl Monkey {
+    fn parse(i: &str) -> IResult<&str, (Monkey, Vec<usize>)> {
+        let (i, _) = tag("Monkey ")(i)?;
+        let (i, _) = digit0(i)?;
+        let (i, _) = tag(":\n  Starting items: ")(i)?;
+        let (i, items) = separated_list0(tag(", "), u32)(i)?;
+        let (i, _) = tag("\n  Operation: new = ")(i)?;
+        let (i, op) = Operation::parse(i)?;
+        let (i, _) = take_until("\n")(i)?;
+        let (i, _) = tag("\n  Test: divisible by ")(i)?;
+        let (i, test) = u32(i)?;
+        let (i, _) = tag("\n    If true: throw to monkey ")(i)?;
+        let (i, monkey_t) = u32(i)?;
+        let (i, _) = tag("\n    If false: throw to monkey ")(i)?;
+        let (i, monkey_f) = u32(i)?;
+
+        Ok((
+            i,
+            (
+                Monkey {
+                    op,
+                    test: test as usize,
+                    next_monkey: (monkey_t as usize, monkey_f as usize),
+                },
+                items.into_iter().map(|x| x as usize).collect(),
+            ),
+        ))
+    }
+
+    fn do_op(&self, x: usize) -> usize {
+        match self.op {
+            Operation::Square => x * x,
+            Operation::Add(c) => x + c,
+            Operation::Mult(c) => x * c,
+        }
+    }
+    fn throw_to(&self, x: usize) -> usize {
+        if (x % self.test) == 0 {
+            self.next_monkey.0
+        } else {
+            self.next_monkey.1
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Operation {
+    Square,
+    Add(usize),
+    Mult(usize),
+}
+
+impl Operation {
+    fn parse(i: &str) -> IResult<&str, Operation> {
+        let (i, _) = tag("old ")(i)?;
+        let (i, op) = alt((tag("* "), tag("+ ")))(i)?;
+        if let Ok((i, _)) = tag::<&str, &str, (&str, nom::error::ErrorKind)>("old")(i) {
+            Ok((i, Operation::Square))
+        } else {
+            let (i, x) = u32(i)?;
+            Ok((
+                i,
+                match op {
+                    "* " => Operation::Mult(x as usize),
+                    "+ " => Operation::Add(x as usize),
+                    _ => unreachable!(),
+                },
+            ))
+        }
+    }
+}