1 files changed, 181 insertions, 0 deletions
diff --git a/src/bin/day11.rs b/src/bin/day11.rs
new file mode 100644
index 0000000..ef77368
--- /dev/null
+++ b/src/bin/day11.rs
@@ -0,0 +1,181 @@
+static DAY: u8 = 11;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", monkey_business(&input, 20, false));
+    println!("{DAY}b: {}", monkey_business(&input, 10000, true));
+}
+
+#[derive(Debug, Clone)]
+enum Operation {
+    Add { operand: Option<usize> },
+    Mul { operand: Option<usize> },
+}
+
+impl Operation {
+    fn new(input: &str) -> Operation {
+        let fixed = "  Operation: new = old ";
+        let mut it = input.chars().skip(fixed.len());
+        let operation = it.next().unwrap();
+        it.next(); // space
+        let operand = it.collect::<String>();
+        let operand = operand.parse::<usize>().ok();
+        match operation {
+            '+' => Operation::Add { operand },
+            '*' => Operation::Mul { operand },
+            _ => unimplemented!(),
+        }
+    }
+
+    fn compute(&self, old: usize) -> usize {
+        match *self {
+            Operation::Add { operand: None } => old + old,
+            Operation::Add { operand: Some(operand) } => old + operand,
+            Operation::Mul { operand: None } => old * old,
+            Operation::Mul { operand: Some(operand) } => old * operand,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Test {
+    divisible: usize,
+    iftrue: usize,
+    iffalse: usize,
+}
+
+impl Test {
+    fn new(input: &[String]) -> Test {
+        let fixed1 = "  Test: divisible by ";
+        let divisible = input[0].chars()
+                                .skip(fixed1.len())
+                                .collect::<String>()
+                                .parse().unwrap();
+
+        let fixed2 = "    If true: throw to monkey ";
+        let iftrue = input[1].chars()
+                             .nth(fixed2.len()).unwrap()
+                             .to_digit(10).unwrap() as usize;
+        let iffalse = input[2].chars()
+                              .nth(fixed2.len() + 1).unwrap()
+                              .to_digit(10).unwrap() as usize;
+
+        Test { divisible, iftrue, iffalse }
+    }
+
+    fn eval(&self, operand: usize) -> usize {
+        if operand % self.divisible == 0 {
+            self.iftrue
+        } else {
+            self.iffalse
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Monkey {
+    items: Vec<usize>,
+    operation: Operation,
+    test: Test,
+    inspections: usize,
+}
+
+impl Monkey {
+    fn new(input: &[String]) -> Monkey {
+        /*let id = input[0].chars()
+                         .skip(7)
+                         .next().unwrap()
+                         .to_digit(10).unwrap();*/
+
+        let items = input[1].split_once(':').unwrap().1
+                            .split(',')
+                            .map(|x| x.trim().parse().unwrap())
+                            .collect();
+
+        let operation = Operation::new(&input[2]);
+
+        let test = Test::new(&input[3..]);
+
+        Monkey { items, operation, test, inspections: 0 }
+    }
+}
+
+fn monkey_business(input: &[String], rounds: usize, worried: bool) -> usize {
+    let mut monkeys = Vec::new();
+    for lines in input.chunks(7) {
+        let monkey = Monkey::new(lines);
+        monkeys.push(monkey);
+    }
+
+    let divisibility : usize = monkeys.iter()
+                                      .map(|m| m.test.divisible)
+                                      .product();
+    for _ in 0 .. rounds {
+        for i in 0 .. monkeys.len() {
+            for item in monkeys[i].items.clone() {
+                monkeys[i].inspections += 1;
+                let mut worry = monkeys[i].operation.compute(item);
+                if !worried {
+                    worry /= 3;
+                } else {
+                    /* all divisibility tests are prime, so it's possible
+                       to reduce the worry level by the product of all values */
+                    worry %= divisibility;
+                }
+                let next = monkeys[i].test.eval(worry);
+                monkeys[next].items.push(worry);
+            }
+            monkeys[i].items.clear();
+        }
+    }
+
+    let mut inspections = monkeys.iter()
+                                 .map(|m| m.inspections)
+                                 .collect::<Vec<_>>();
+    inspections.sort();
+    inspections.iter()
+               .rev()
+               .take(2)
+               .product()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "Monkey 0:",
+            "  Starting items: 79, 98",
+            "  Operation: new = old * 19",
+            "  Test: divisible by 23",
+            "    If true: throw to monkey 2",
+            "    If false: throw to monkey 3",
+            "",
+            "Monkey 1:",
+            "  Starting items: 54, 65, 75, 74",
+            "  Operation: new = old + 6",
+            "  Test: divisible by 19",
+            "    If true: throw to monkey 2",
+            "    If false: throw to monkey 0",
+            "",
+            "Monkey 2:",
+            "  Starting items: 79, 60, 97",
+            "  Operation: new = old * old",
+            "  Test: divisible by 13",
+            "    If true: throw to monkey 1",
+            "    If false: throw to monkey 3",
+            "",
+            "Monkey 3:",
+            "  Starting items: 74",
+            "  Operation: new = old + 3",
+            "  Test: divisible by 17",
+            "    If true: throw to monkey 0",
+            "    If false: throw to monkey 1",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+
+        assert_eq!(monkey_business(&input, 20, false), 10605);
+        assert_eq!(monkey_business(&input, 10000, true), 2713310158);
+    }
+}