Day 20 - Part 2

Signed-off-by: Anthony Oteri <anthony.oteri@gmail.com>

day-20/src/part2.rs

@@ -1,18 +1,286 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{alpha1, line_ending},
+    multi::separated_list1,
+    sequence::preceded,
+    IResult,
+};
+
 use crate::error::AocError;
 
-#[tracing::instrument]
-pub fn process(input: &str) -> miette::Result<u64, AocError> {
-    Ok(0)
+#[derive(Debug)]
+enum State {
+    On,
+    Off,
 }
 
+#[derive(Debug, Copy, Clone)]
+enum Signal {
+    High,
+    Low,
+}
+
+#[derive(Debug)]
+enum ModuleType<'a> {
+    Broadcaster,
+    FlipFlop { state: State },
+    Conjunction { inputs: HashMap<&'a str, Signal> },
+    Test,
+}
+
+#[derive(Debug)]
+struct Module<'a> {
+    id: &'a str,
+    module_type: ModuleType<'a>,
+    outputs: Vec<&'a str>,
+}
+
+impl<'a> Module<'a> {
+    #[tracing::instrument]
+    fn process(&mut self, from: &'a str, signal: &Signal) -> Vec<(&'a str, &'a str, Signal)> {
+        match (&mut self.module_type, signal) {
+            (ModuleType::Broadcaster, signal) => self
+                .outputs
+                .iter()
+                .map(|o| (self.id, *o, *signal))
+                .collect(),
+            (ModuleType::FlipFlop { .. }, Signal::High) => {
+                vec![]
+            }
+            (ModuleType::FlipFlop { state: State::On }, Signal::Low) => {
+                self.module_type = ModuleType::FlipFlop { state: State::Off };
+                self.outputs
+                    .iter()
+                    .map(|o| (self.id, *o, Signal::Low))
+                    .collect()
+            }
+            (ModuleType::FlipFlop { state: State::Off }, Signal::Low) => {
+                self.module_type = ModuleType::FlipFlop { state: State::On };
+                self.outputs
+                    .iter()
+                    .map(|o| (self.id, *o, Signal::High))
+                    .collect()
+            }
+            (ModuleType::Conjunction { ref mut inputs }, pulse) => {
+                inputs.entry(from).and_modify(|s| *s = *pulse);
+                if inputs.values().all(|s| matches!(s, Signal::High)) {
+                    self.outputs
+                        .iter()
+                        .map(|o| (self.id, *o, Signal::Low))
+                        .collect()
+                } else {
+                    self.outputs
+                        .iter()
+                        .map(|o| (self.id, *o, Signal::High))
+                        .collect()
+                }
+            }
+            _ => {
+                vec![]
+            }
+        }
+    }
+}
+
+fn broadcaster(input: &str) -> IResult<&str, Module> {
+    let (input, id) = alpha1(input)?;
+    let (input, _) = tag(" -> ")(input)?;
+    let (input, outputs) = separated_list1(tag(", "), alpha1)(input)?;
+
+    Ok((
+        input,
+        Module {
+            id,
+            module_type: ModuleType::Broadcaster,
+            outputs,
+        },
+    ))
+}
+
+fn flip_flop(input: &str) -> IResult<&str, Module> {
+    let (input, id) = preceded(nom::character::complete::char('%'), alpha1)(input)?;
+    let (input, _) = tag(" -> ")(input)?;
+    let (input, outputs) = separated_list1(tag(", "), alpha1)(input)?;
+
+    Ok((
+        input,
+        Module {
+            id,
+            module_type: ModuleType::FlipFlop { state: State::Off },
+            outputs,
+        },
+    ))
+}
+
+fn conjunction(input: &str) -> IResult<&str, Module> {
+    let (input, id) = preceded(nom::character::complete::char('&'), alpha1)(input)?;
+    let (input, _) = tag(" -> ")(input)?;
+    let (input, outputs) = separated_list1(tag(", "), alpha1)(input)?;
+
+    Ok((
+        input,
+        Module {
+            id,
+            module_type: ModuleType::Conjunction {
+                inputs: HashMap::new(),
+            },
+            outputs,
+        },
+    ))
+}
+
+fn parser(input: &str) -> IResult<&str, HashMap<&str, Module>> {
+    let (input, modules) =
+        separated_list1(line_ending, alt((broadcaster, flip_flop, conjunction)))(input)?;
+
+    let mut module_map = modules
+        .into_iter()
+        .map(|m| (m.id, m))
+        .collect::<HashMap<&str, Module>>();
+
+    let conjunctions: Vec<&str> = module_map
+        .iter()
+        .filter(|(_, m)| matches!(m.module_type, ModuleType::Conjunction { .. }))
+        .map(|(id, _)| *id)
+        .collect();
+
+    let all_inputs: HashSet<&str> = module_map.keys().copied().collect();
+    let all_outputs: HashSet<&str> = module_map
+        .iter()
+        .flat_map(|(_, m)| m.outputs.iter().copied())
+        .collect();
+    for module in all_outputs.difference(&all_inputs) {
+        module_map.entry(module).or_insert(Module {
+            id: module,
+            module_type: ModuleType::Test,
+            outputs: Vec::default(),
+        });
+    }
+
+    for conjunction in conjunctions {
+        let inputs: Vec<&str> = module_map
+            .iter()
+            .filter(|(_, m)| m.outputs.contains(&conjunction))
+            .map(|(id, _)| *id)
+            .collect();
+
+        for input in inputs {
+            module_map.entry(conjunction).and_modify(|m| {
+                if let ModuleType::Conjunction { inputs, .. } = &mut m.module_type {
+                    inputs.insert(input, Signal::Low);
+                }
+            });
+        }
+    }
+
+    Ok((input, module_map))
+}
+
+#[tracing::instrument(skip(input))]
+pub fn process(input: &str) -> miette::Result<u64, AocError> {
+    let (input, mut modules) = parser(input).unwrap();
+    debug_assert!(input.is_empty());
+
+    let target = modules
+        .iter()
+        .filter_map(|(id, m)| match m.module_type {
+            ModuleType::Test => Some(*id),
+            _ => None,
+        })
+        .next()
+        .unwrap();
+
+    let target_parents = modules
+        .iter()
+        .filter_map(|(id, m)| {
+            if m.outputs.contains(&target) {
+                Some(*id)
+            } else {
+                None
+            }
+        })
+        .collect::<Vec<&str>>();
+
+    let mut target_grandparents = target_parents
+        .iter()
+        .flat_map(|p| {
+            modules
+                .iter()
+                .filter_map(|(gp, m)| {
+                    if m.outputs.contains(p) {
+                        Some(*gp)
+                    } else {
+                        None
+                    }
+                })
+                .collect::<Vec<&str>>()
+        })
+        .collect::<Vec<&str>>();
+
+    let mut loops: HashMap<&str, usize> = HashMap::default();
+
+    for i in 1.. {
+        let mut queue = VecDeque::new();
+        queue.push_back(("button", "broadcaster", Signal::Low));
+
+        loop {
+            if queue.is_empty() {
+                break;
+            }
+            let (from, to, signal) = queue.pop_front().unwrap();
+            if target_grandparents.contains(&to) && matches!(signal, Signal::Low) {
+                loops.insert(to, i);
+                target_grandparents.retain(|gp| *gp != to);
+            }
+
+            tracing::info!("{} -{:?}-> {}", from, signal, to);
+            let module = modules.get_mut(to).unwrap();
+            let signals = module.process(from, &signal);
+            queue.extend(signals);
+        }
+
+        if target_grandparents.is_empty() {
+            break;
+        }
+    }
+
+    dbg!(&loops);
+
+    Ok(lcm(&loops.values().copied().collect::<Vec<usize>>()) as u64)
+}
+
+fn lcm(nums: &[usize]) -> usize {
+    if nums.len() == 1 {
+        return nums[0];
+    }
+    let a = nums[0];
+    let b = lcm(&nums[1..]);
+    a * b / gcd(a, b)
+}
+
+fn gcd(a: usize, b: usize) -> usize {
+    if b == 0 {
+        return a;
+    }
+    gcd(b, a % b)
+}
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    #[test_log::test]
-    fn test_process() -> miette::Result<()> {
-        let input = include_str!("../test-input.txt");
-        assert_eq!(0, process(input)?);
+    use rstest::rstest;
+
+    #[test_log::test(rstest)]
+    #[case("test-input2.txt", 11687500)]
+    fn test_process(#[case] filename: &str, #[case] expected: u64) -> miette::Result<()> {
+        let input =
+            String::from_utf8_lossy(&std::fs::read(std::path::Path::new(filename)).unwrap())
+                .parse::<String>()
+                .unwrap();
+        assert_eq!(expected, process(&input)?);
         Ok(())
     }
 }