Day 11, puzzle 2

src/bin/d11p1.rs

@@ -10,8 +10,8 @@ pub fn main() {
 
     let monkeys = day11::parse_monkeys(&util::parse_input());
 
-    for _ in 0..20 {
-        day11::do_round(&monkeys);
+    for _ in 0..N_ROUNDS {
+        day11::do_round(&monkeys, true);
     }
 
     println!(

src/bin/d11p2.rs

@@ -0,0 +1,22 @@
+use aoc22::{
+    day11::{self, monkey_business},
+    util,
+};
+
+const N_ROUNDS: usize = 10000;
+
+pub fn main() {
+    env_logger::init();
+
+    let monkeys = day11::parse_monkeys(&util::parse_input());
+
+    for _ in 0..N_ROUNDS {
+        day11::do_round(&monkeys, false);
+    }
+
+    println!(
+        "Monkey business after {} rounds is {}",
+        N_ROUNDS,
+        monkey_business(&monkeys)
+    );
+}

src/day11.rs

@@ -1,6 +1,7 @@
-use std::{borrow::BorrowMut, cell::RefCell, collections::VecDeque};
+use std::{cell::RefCell, collections::VecDeque};
 
 use itertools::Itertools;
+use num::Integer;
 use regex::Regex;
 
 #[derive(Debug)]
@@ -137,7 +138,12 @@ fn parse_op_kind(s: &str) -> OpKind {
     }
 }
 
-pub fn do_round(monkeys: &Vec<RefCell<Monkey>>) {
+pub fn do_round(monkeys: &Vec<RefCell<Monkey>>, do_worry: bool) {
+    let overall_mod = monkeys
+        .iter()
+        .map(|m| m.borrow().test.div)
+        .reduce(|acc, div| acc.lcm(&div))
+        .unwrap();
     for n in 0..monkeys.len() {
         let mut monkey = monkeys.get(n).unwrap().borrow_mut();
         log::debug!("Monkey {}", n);
@@ -145,21 +151,23 @@ pub fn do_round(monkeys: &Vec<RefCell<Monkey>>) {
             monkey.activity += 1;
             let mut item = monkey.items.pop_front().unwrap();
             log::debug!("  Monkey inspects an item with a worry level of {}.", item);
-            item = run_op(&monkey.op, item);
+            item = run_op(&monkey.op, item) % overall_mod;
             log::debug!("    Worry level increases to {}.", item);
-            item /= 3;
-            log::debug!(
-                "    Monkey gets bored with item. Worry level is divided by 3 to {}.",
-                item
-            );
+            if do_worry {
+                item /= 3;
+                log::debug!(
+                    "    Monkey gets bored with item. Worry level is divided by 3 to {}.",
+                    item
+                );
+            }
             let target = if item % monkey.test.div == 0 {
+                log::debug!("Current worry level is divisible by {}", monkey.test.div);
+                monkey.test.target_true
+            } else {
                 log::debug!(
                     "Current worry level is not divisible by {}",
                     monkey.test.div
                 );
-                monkey.test.target_true
-            } else {
-                log::debug!("Current worry level is divisible by {}", monkey.test.div);
                 monkey.test.target_false
             };
             log::debug!(