[rs] Solve 2022_11 part 2

inputs/2022/2022_11.solution

@@ -1,2 +1,2 @@
 Part 1: 66124
-Part 2: ???
+Part 2: 19309892877

rs/src/y2022/d11.rs

@@ -1,14 +1,14 @@
 use std::mem;
 use std::str::Lines;
 
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 enum Operation {
     Add,
     Mul,
 }
 
 impl Operation {
-    fn eval(self, lhs: u32, rhs: u32) -> u32 {
+    fn eval(self, lhs: u64, rhs: u64) -> u64 {
         match self {
             Self::Add => lhs + rhs,
             Self::Mul => lhs * rhs,
@@ -16,14 +16,15 @@ impl Operation {
     }
 }
 
+#[derive(Clone)]
 struct Monkey {
-    holds: Vec<u32>,
+    holds: Vec<u64>,
 
     // Left hand side is always "old"
     op: Operation,
-    rhs: Option<u32>,
+    rhs: Option<u64>,
 
-    div_by: u32,
+    div_by: u64,
     if_true: usize,
     if_false: usize,
 
@@ -41,7 +42,7 @@ impl Monkey {
 
         let holds = prefixed(&mut lines, "  Starting items: ")
             .split(", ")
-            .map(|i| i.parse::<u32>().unwrap())
+            .map(|i| i.parse::<u64>().unwrap())
             .collect::<Vec<_>>();
 
         let (op, rhs) = prefixed(&mut lines, "  Operation: new = old ")
@@ -93,12 +94,14 @@ impl Monkey {
     }
 }
 
-fn round(monkeys: &mut Vec<Monkey>) {
+fn round(monkeys: &mut Vec<Monkey>, reduce_worry: bool, modulo: u64) {
     for i in 0..monkeys.len() {
         monkeys[i].inspections += monkeys[i].holds.len();
         let monkey = monkeys[i].take();
         for item in monkey.holds {
-            let item = monkey.op.eval(item, monkey.rhs.unwrap_or(item)) / 3;
+            let item = monkey.op.eval(item, monkey.rhs.unwrap_or(item));
+            let item = if reduce_worry { item / 3 } else { item };
+            let item = item % modulo;
             let target = if item % monkey.div_by == 0 {
                 monkey.if_true
             } else {
@@ -109,18 +112,30 @@ fn round(monkeys: &mut Vec<Monkey>) {
     }
 }
 
+fn monkey_business(monkeys: &[Monkey]) -> usize {
+    let mut inspections = monkeys.iter().map(|m| m.inspections).collect::<Vec<_>>();
+    inspections.sort_unstable();
+    inspections.into_iter().rev().take(2).product::<usize>()
+}
+
 pub fn solve(input: String) {
     let mut monkeys = vec![];
     for monkey in input.trim().split("\n\n") {
         monkeys.push(Monkey::parse(monkey));
     }
 
-    for _ in 0..20 {
-        round(&mut monkeys);
-    }
+    let common_multiple = monkeys.iter().map(|m| m.div_by).product::<u64>();
+    eprintln!("Common multiple: {common_multiple}");
 
-    let mut inspections = monkeys.iter().map(|m| m.inspections).collect::<Vec<_>>();
-    inspections.sort_unstable();
-    let part1 = inspections.into_iter().rev().take(2).product::<usize>();
-    println!("Part 1: {part1}");
+    let mut part1 = monkeys.clone();
+    for _ in 0..20 {
+        round(&mut part1, true, common_multiple);
+    }
+    println!("Part 1: {}", monkey_business(&part1));
+
+    let mut part2 = monkeys.clone();
+    for _ in 0..10000 {
+        round(&mut part2, false, common_multiple);
+    }
+    println!("Part 2: {}", monkey_business(&part2));
 }

sample_inputs/2022/2022_11.solution

@@ -1,2 +1,2 @@
 Part 1: 10605
-Part 2: ???
+Part 2: 2713310158