day(20): add solution

Signed-off-by: Matej Focko <me@mfocko.xyz>

samples/day20.txt

@@ -0,0 +1,5 @@
+broadcaster -> a
+%a -> inv, con
+&inv -> b
+%b -> con
+&con -> output

src/bin/day20.rs

@@ -0,0 +1,227 @@
+use std::{
+    collections::{HashMap, HashSet, VecDeque},
+    hash::{DefaultHasher, Hash, Hasher},
+    str::FromStr,
+};
+
+use aoc_2023::*;
+
+type Output1 = usize;
+type Output2 = Output1;
+
+lazy_static! {
+    static ref GATE_REGEX: Regex = Regex::new(r"([%&]?)(.*) -> (.*)").unwrap();
+}
+
+fn gate_hash(name: &str) -> u64 {
+    let mut h = DefaultHasher::new();
+    name.hash(&mut h);
+    h.finish()
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum GateState {
+    Repeater,
+    FlipFlop(bool),
+    Nand(u32),
+}
+
+impl FromStr for GateState {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        match s {
+            "" => Ok(GateState::Repeater),
+            "%" => Ok(GateState::FlipFlop(false)),
+            "&" => Ok(GateState::Nand(0)),
+            _ => Err("Invalid kind"),
+        }
+    }
+}
+
+impl GateState {
+    fn exec(
+        &mut self,
+        watch: Option<u64>,
+        src: u64,
+        dest: &Gate,
+        p: bool,
+    ) -> Option<(Option<usize>, bool)> {
+        match self {
+            GateState::Repeater => Some((None, p)),
+            GateState::FlipFlop(b) => {
+                if p {
+                    None
+                } else {
+                    *b = !*b;
+                    Some((None, *b))
+                }
+            }
+            GateState::Nand(v) => {
+                let idx = dest
+                    .inputs
+                    .iter()
+                    .position(|i| gate_hash(i) == src)
+                    .unwrap();
+
+                let mut high = None;
+                if p {
+                    if watch.is_some_and(|h| dest.hash == h) {
+                        high = Some(idx);
+                    }
+
+                    *v |= 1 << idx;
+                } else {
+                    *v &= !(1 << idx);
+                }
+
+                Some((high, *v != (1 << dest.inputs.len()) - 1))
+            }
+        }
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+struct Gate {
+    inputs: Vec<String>,
+    outputs: Vec<String>,
+    hash: u64,
+}
+
+impl Gate {
+    fn new(name: &str) -> Gate {
+        Gate {
+            inputs: vec![],
+            outputs: vec![],
+            hash: gate_hash(name),
+        }
+    }
+}
+
+struct Day20 {
+    gates: HashMap<String, Gate>,
+    initial_state: HashMap<String, GateState>,
+}
+
+impl Day20 {
+    fn push(
+        &self,
+        state: &mut HashMap<String, GateState>,
+        watch: Option<u64>,
+    ) -> (usize, usize, Option<usize>) {
+        let mut q = VecDeque::new();
+        let mut counters = vec![0, 0];
+        let mut high_idx = None;
+
+        q.push_back(("button".to_owned(), "broadcaster".to_owned(), false));
+        while let Some((src, dest, pulse)) = q.pop_front() {
+            counters[pulse as usize] += 1;
+
+            let (Some(g), Some(gs)) = (self.gates.get(&dest), state.get_mut(&dest)) else {
+                continue;
+            };
+
+            if let Some((found_idx, next_pulse)) = gs.exec(watch, gate_hash(&src), g, pulse) {
+                if found_idx.is_some() {
+                    high_idx = found_idx;
+                }
+
+                for next_gate in &g.outputs {
+                    q.push_back((dest.clone(), next_gate.clone(), next_pulse));
+                }
+            }
+        }
+
+        (counters[0], counters[1], high_idx)
+    }
+}
+
+impl Solution<Output1, Output2> for Day20 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        let lines: Vec<String> = file_to_lines(pathname);
+
+        let mut gates: HashMap<String, Gate> = HashMap::new();
+        let mut initial_state: HashMap<String, GateState> = HashMap::new();
+
+        for (kind, name, outputs) in lines.into_iter().map(|g| {
+            let (_, [kind, name, outputs]) = GATE_REGEX.captures(&g).unwrap().extract();
+            (
+                kind.to_owned(),
+                name.to_owned(),
+                outputs.split(", ").map(str::to_owned).collect_vec(),
+            )
+        }) {
+            for o in &outputs {
+                gates
+                    .entry(o.clone())
+                    .or_default()
+                    .inputs
+                    .push(name.clone());
+            }
+
+            gates
+                .entry(name.clone())
+                .or_insert(Gate::new(&name))
+                .outputs = outputs;
+            initial_state.insert(name, kind.parse().unwrap());
+        }
+
+        assert_eq!(
+            gates
+                .keys()
+                .map(|k| gate_hash(k))
+                .collect::<HashSet<u64>>()
+                .len(),
+            gates.len(),
+            "no collisions in hash"
+        );
+
+        Self {
+            gates,
+            initial_state,
+        }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        let mut state = self.initial_state.clone();
+        let (mut l, mut h) = (0, 0);
+
+        for _ in 0..1000 {
+            let (l_iter, h_iter, _) = self.push(&mut state, None);
+            l += l_iter;
+            h += h_iter;
+        }
+
+        l * h
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        let rx_parent = &self.gates["rx"].inputs[0];
+        let rx_parent_hash = Some(gate_hash(&rx_parent));
+
+        let mut cycles = vec![0_usize; self.gates[rx_parent].inputs.len()];
+        let mut found = 0;
+
+        let mut state = self.initial_state.clone();
+        for i in 1.. {
+            if found >= cycles.len() {
+                break;
+            }
+
+            if let (_, _, Some(idx)) = self.push(&mut state, rx_parent_hash) {
+                if cycles[idx] == 0 {
+                    cycles[idx] = i;
+                    found += 1;
+                }
+            }
+        }
+
+        cycles.into_iter().product1().unwrap()
+    }
+}
+
+fn main() -> Result<()> {
+    Day20::main()
+}
+
+test_sample!(day_20, Day20, 11687500, 0);