add day 11, part 2

day11/common.rs

@@ -34,6 +34,7 @@ pub struct Monkey {
 
 pub struct Game {
     monkeys: Vec<Monkey>,
+    modulus_lcm: u64,
     divisor: u64,
 }
 
@@ -158,8 +159,10 @@ impl Game {
         while let Some(monkey) = Monkey::from_stdin()? {
             monkeys.push(monkey);
         }
+        let modulus_lcm = monkeys.iter().map(|m| m.modulus).product();
         Ok(Self {
             monkeys: monkeys,
+            modulus_lcm: modulus_lcm,
             divisor: divisor,
         })
     }
@@ -178,7 +181,7 @@ impl Iterator for Game {
                 match self.monkeys[i].throw_item(self.divisor) {
                     Ok(None) => break,
                     Ok(Some((item, target))) => {
-                        self.monkeys[target].add_item(item);
+                        self.monkeys[target].add_item(item % self.modulus_lcm);
                     }
                     Err(e) => return Some(Err(e)),
                 }

day11/part2.rs

@@ -0,0 +1,36 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// usage: ./part1 < input
+
+pub mod common;
+
+use common::{Game, Monkey};
+
+fn main() -> Result<(), &'static str> {
+    let game = Game::from_stdin(1)?;
+    let last_round = game.take(10000).last().unwrap();
+    let mut item_counts: Vec<_> = last_round?
+        .monkeys()
+        .iter()
+        .map(Monkey::item_count)
+        .collect();
+    item_counts.sort();
+    println!(
+        "{}",
+        item_counts[item_counts.len() - 1] * item_counts[item_counts.len() - 2]
+    );
+    Ok(())
+}