1 files changed, 168 insertions, 0 deletions
diff --git a/src/bin/day10.rs b/src/bin/day10.rs
new file mode 100644
index 0000000..d45661e
--- /dev/null
+++ b/src/bin/day10.rs
@@ -0,0 +1,168 @@
+use std::collections::HashMap;
+use std::io::{self, Read};
+use std::str::FromStr;
+
+#[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
+struct Chip(u32);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+struct Bot(u32);
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+struct Output(u32);
+
+#[derive(Clone, Copy, Default)]
+struct BotChips(Option<Chip>, Option<Chip>);
+
+impl BotChips {
+    fn add(&mut self, chip: Chip) {
+        match (self.0, self.1) {
+            (None, None) => {
+                self.0 = Some(chip);
+            },
+            (Some(low), None) if low < chip => {
+                self.1 = Some(chip);
+            },
+            (Some(high), None) => {
+                self.0 = Some(chip);
+                self.1 = Some(high);
+            },
+            _ => panic!("bot has too many chips"),
+        }
+    }
+
+    fn has_two(&self) -> bool {
+        self.0.is_some() && self.1.is_some()
+    }
+}
+
+#[derive(Clone, Copy)]
+enum Destination {
+    Bot(Bot),
+    Output(Output),
+}
+
+impl Destination {
+    fn from_pair(ty: &str, value: u32) -> Result<Self, ()> {
+        match ty {
+            "bot" => Ok(Destination::Bot(Bot(value))),
+            "output" => Ok(Destination::Output(Output(value))),
+            _ => Err(()),
+        }
+    }
+}
+
+#[derive(Default)]
+struct Instructions {
+    chips: HashMap<Chip, Bot>,
+    bots: HashMap<Bot, (Destination, Destination)>,
+}
+
+impl FromStr for Instructions {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Self, ()> {
+        let mut instructions = Instructions::default();
+
+        for line in s.lines() {
+            let mut words = line.split(' ');
+            if words.next() == Some("value") {
+                let value = words.next().ok_or(())?.parse().map_err(|_| ())?;
+                let bot = words.nth(3).ok_or(())?.parse().map_err(|_| ())?;
+
+                instructions.chips.insert(Chip(value), Bot(bot));
+            } else {
+                let bot = words.next().ok_or(())?.parse().map_err(|_| ())?;
+                let low_type = words.nth(3).ok_or(())?;
+                let low_value = words.next().ok_or(())?.parse().map_err(|_| ())?;
+                let high_type = words.nth(3).ok_or(())?;
+                let high_value = words.next().ok_or(())?.parse().map_err(|_| ())?;
+
+                let low = Destination::from_pair(low_type, low_value)?;
+                let high = Destination::from_pair(high_type, high_value)?;
+
+                instructions.bots.insert(Bot(bot), (low, high));
+            }
+        }
+
+        Ok(instructions)
+    }
+}
+
+#[derive(Default)]
+struct State {
+    outputs: HashMap<Output, Vec<Chip>>,
+    bots: HashMap<Bot, BotChips>,
+    comparisons: HashMap<(Chip, Chip), Bot>,
+}
+
+impl State {
+    fn initialize(&mut self, instructions: &Instructions) {
+        for (&chip, &bot) in &instructions.chips {
+            self.bots.entry(bot).or_insert_with(Default::default).add(chip);
+        }
+    }
+
+    fn step(&mut self, instructions: &Instructions) -> bool {
+        let active_bots: Vec<Bot> = self.bots.iter()
+            .filter(|&(_, ref chips)| chips.has_two())
+            .map(|(&bot, _)| bot)
+            .collect();
+
+        if active_bots.is_empty() {
+            return false;
+        }
+
+        for bot in active_bots {
+            let (low, high) = {
+                let chips = self.bots.get_mut(&bot).unwrap();
+                (chips.0.take().unwrap(), chips.1.take().unwrap())
+            };
+            self.comparisons.insert((low, high), bot);
+
+            let &(low_dest, high_dest) = instructions.bots.get(&bot).unwrap();
+            self.add_to(low_dest, low);
+            self.add_to(high_dest, high);
+        }
+
+        true
+    }
+
+    fn add_to(&mut self, destination: Destination, chip: Chip) {
+        match destination {
+            Destination::Bot(bot) => {
+                self.bots.entry(bot).or_insert_with(Default::default).add(chip);
+            },
+            Destination::Output(output) => {
+                self.outputs.entry(output).or_insert_with(Vec::new).push(chip);
+            },
+        }
+    }
+}
+
+fn solve(comparison: (Chip, Chip), input: &str) -> Option<Bot> {
+    let instructions = input.parse().unwrap();
+    let mut state = State::default();
+    state.initialize(&instructions);
+    while state.step(&instructions) { }
+    state.comparisons.get(&comparison).cloned()
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {:?}", solve((Chip(17), Chip(61)), &input));
+}
+
+#[test]
+fn part1() {
+    let input = "
+value 5 goes to bot 2
+bot 2 gives low to bot 1 and high to bot 0
+value 3 goes to bot 1
+bot 1 gives low to output 1 and high to bot 0
+bot 0 gives low to output 2 and high to output 0
+value 2 goes to bot 2
+";
+    assert_eq!(Some(Bot(2)), solve((Chip(2), Chip(5)), input.trim()));
+}