diff --git a/20/day20.rs b/20/day20.rs
new file mode 100644
index 0000000..8cf8517
--- /dev/null
+++ b/20/day20.rs
@@ -0,0 +1,146 @@
+use std::io::{self, BufRead};
+use std::convert::TryInto;
+// use num::Integer;
+use std::collections::{HashMap, VecDeque};
+
+type Pulse = u8;
+const LOW: Pulse = 0;
+const HIGH: Pulse = 1;
+
+trait Module {
+    fn get_pulse(&mut self, from: u16, pulse: Pulse) -> Option<Pulse>;
+    fn add_input(&mut self, input: u16) {}
+    fn get_connections(&self) -> &Vec<u16>;
+}
+#[derive(Clone)]
+struct FlipFlop {
+    name: u16,
+    modules: Vec<u16>,
+    state: Pulse,
+}
+impl Module for FlipFlop {
+    fn get_pulse(&mut self, from: u16, pulse: Pulse) -> Option<Pulse> {
+        if pulse == LOW {
+            self.state ^= HIGH;
+            return Some(self.state);
+        }
+        None
+    }
+    fn get_connections(&self) -> &Vec<u16> { return &self.modules; }
+}
+
+#[derive(Clone)]
+struct Conjunction {
+    name: u16,
+    modules: Vec<u16>,
+    state: Pulse,
+    last_inputs: HashMap<u16, Pulse>,
+}
+impl Module for Conjunction {
+    fn get_pulse(&mut self, from: u16, pulse: Pulse) -> Option<Pulse> {
+        self.last_inputs.iter().for_each(|(k, v)| print!("{}: {},", k, v));
+        println!();
+        if !self.last_inputs.contains_key(&from) {
+            panic!("Conjunction got unexpected impulse from {}", from);
+        }
+        *self.last_inputs.get_mut(&from).unwrap() = pulse;
+        if self.last_inputs.iter().all(|(k,v)| *v == HIGH) { self.state = LOW; }
+        else { self.state = HIGH; }
+        return Some(self.state)
+    }
+    fn add_input(&mut self, input: u16) {
+        self.last_inputs.insert(input, LOW);
+    }
+    fn get_connections(&self) -> &Vec<u16> { return &self.modules; }
+}
+
+#[derive(Clone)]
+struct Start {
+    name: u16,
+    modules: Vec<u16>,
+    state: Pulse,
+}
+impl Module for Start {
+    fn get_pulse(&mut self, from: u16, pulse: Pulse) -> Option<Pulse> {
+        self.state = pulse;
+        return Some(self.state)
+    }
+    fn get_connections(&self) -> &Vec<u16> { return &self.modules; }
+}
+
+
+fn make_index(s: &str) -> u16 {
+    println!("{}", s);
+    if s.len() == 2 {
+        let mut t: u16 = 0; 
+        s.as_bytes().iter().enumerate().for_each(|(i, c)| t |= (*c as u16) << i*8);
+        return t;
+    }
+    return 0
+}
+fn from_index(i: u16) -> char {
+    if i == 0 { return 'B' }
+    let mut c: u8 = i as u8;
+    c |= i.overflowing_shr(8).0 as u8;
+    return c as char
+}
+
+fn main() {
+    let input = "input.txt";
+    // let input = "example.txt";
+    // let input = "example2.txt";
+    let mut lines = read_lines(&input);
+    let mut modules = HashMap::<u16, Box<dyn Module>>::new();
+    for line in lines.map(|r| r.ok().unwrap()) {
+        let dash = line.find('-').unwrap();
+        let module = make_index(&line[1..dash-1]);
+        println!("{module}");
+        let connected_modules = line[dash+2..].split(',').map(|s| make_index(&s[1..])).collect();
+        let _ = match line.chars().next().unwrap() {
+            '&' => modules.insert(module, Box::new(Conjunction{name:module, modules: connected_modules, state: LOW, last_inputs: HashMap::new()})),
+            '%' => modules.insert(module, Box::new(FlipFlop{name:module, modules: connected_modules, state: LOW})),
+            _   => modules.insert(module, Box::new(Start{name:module, modules: connected_modules, state: LOW})),
+        };
+    }
+    let keys = modules.keys().map(|k| *k).collect::<Vec<u16>>().clone();
+    for n in keys.iter() {
+        let connected_modules = modules[n].get_connections().clone().iter().filter(|c| modules.contains_key(c)).map(|c| *c).collect::<Vec<u16>>();
+        for c in connected_modules.iter() {
+            let m = modules.get_mut(c).unwrap();
+            m.add_input(*n);
+        }
+    }
+    let mut modules2 = modules.clone();
+    let mut queue: VecDeque::<(u16, Pulse)> = VecDeque::new();
+    let mut lows: usize = 0;
+    let mut highs: usize = 0;
+    for i in 0..1000 {
+        println!("{i}");
+        queue.push_back((0, LOW));
+        lows += 1;
+        while !queue.is_empty() {
+            let (from, pulse) = queue.pop_front().unwrap();
+            if !modules.contains_key(&from) { continue; }
+            for m in modules[&from].get_connections().clone().iter() {
+                println!("{:6} -{} -> {}", from_index(from), pulse, from_index(*m));
+                if pulse == LOW { lows += 1 } else { highs += 1 }
+                if !modules.contains_key(m) { continue; }
+                if let Some(new_pulse) = modules.get_mut(&m).unwrap().get_pulse(from, pulse) {
+                    queue.push_back((*m, new_pulse));
+                }
+            }
+        }
+    }
+    println!("lows: {}, highs: {}", lows, highs);
+    println!("lows * highs (1): {}", lows * highs);
+
+}
+
+
+fn read_lines<P>(filename: P) -> io::Lines<io::BufReader<std::fs::File>>
+where P: AsRef<std::path::Path>, {
+    return match std::fs::File::open(filename) {
+        Err(why) => panic!("Could not open file. {}", why),
+        Ok(file) => std::io::BufReader::new(file).lines()
+    };
+}