diff --git a/2023/Cargo.toml b/2023/Cargo.toml
index 21401dd..07c51de 100644
--- a/2023/Cargo.toml
+++ b/2023/Cargo.toml
@@ -21,7 +21,7 @@ members = [
   "day17",
   "day18",
   "day19",
-  # "day20",
+  "day20",
   # "day21",
   # "day22",
   # "day23",
diff --git a/2023/day19/map+sum b/2023/day19/map+sum
deleted file mode 100644
index e69de29..0000000
diff --git a/2023/day20/.gitignore b/2023/day20/.gitignore
new file mode 100644
index 0000000..e983cca
--- /dev/null
+++ b/2023/day20/.gitignore
@@ -0,0 +1,19 @@
+input.txt
+flamegraph.svg
+perf.data*
+### Rust
+# Generated by Cargo
+# will have compiled files and executables
+debug/
+target/
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb
+
diff --git a/2023/day20/Cargo.toml b/2023/day20/Cargo.toml
new file mode 100644
index 0000000..7317983
--- /dev/null
+++ b/2023/day20/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day20"
+authors = ["mirsella <mirsella@protonmail.com>"]
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
diff --git a/2023/day20/build.rs b/2023/day20/build.rs
new file mode 100644
index 0000000..b6a19a0
--- /dev/null
+++ b/2023/day20/build.rs
@@ -0,0 +1,28 @@
+use std::fs::File;
+use std::io::{self, Read};
+use std::path::PathBuf;
+use std::{env, fs};
+
+fn replace_in_file(file_path: &PathBuf, old: &str, new: &str) -> io::Result<()> {
+    let mut contents = String::new();
+    File::open(file_path)?.read_to_string(&mut contents)?;
+    let new_contents = contents.replace(old, new);
+    if contents != new_contents {
+        println!("Updating {}", file_path.display());
+        fs::write(file_path, new_contents)?;
+    }
+    Ok(())
+}
+
+fn main() -> io::Result<()> {
+    let pkg_name = env::var("CARGO_PKG_NAME").unwrap();
+    replace_in_file(
+        &"../Cargo.toml".into(),
+        &format!("# \"{pkg_name}\""),
+        &format!("\"{pkg_name}\""),
+    )?;
+
+    replace_in_file(&"./Cargo.toml".into(), "\n[workspace]", "")?;
+
+    Ok(())
+}
diff --git a/2023/day20/src/main.rs b/2023/day20/src/main.rs
new file mode 100644
index 0000000..f1037b3
--- /dev/null
+++ b/2023/day20/src/main.rs
@@ -0,0 +1,260 @@
+use std::{
+    any::Any,
+    borrow::BorrowMut,
+    cell::{Cell, RefCell},
+    collections::{HashMap, VecDeque},
+    iter,
+    ops::{Add, Not},
+    rc::Rc,
+};
+
+#[derive(Copy, Clone, Hash, PartialEq, Eq, Debug)]
+enum Pulse {
+    High,
+    Low,
+}
+impl Add<Pulse> for (usize, usize) {
+    type Output = (usize, usize);
+    fn add(self, pulse: Pulse) -> Self::Output {
+        match pulse {
+            Pulse::High => (self.0, self.1 + 1),
+            Pulse::Low => (self.0 + 1, self.1),
+        }
+    }
+}
+impl From<Pulse> for bool {
+    fn from(p: Pulse) -> Self {
+        match p {
+            Pulse::High => true,
+            Pulse::Low => false,
+        }
+    }
+}
+impl From<bool> for Pulse {
+    fn from(b: bool) -> Self {
+        match b {
+            true => Self::High,
+            false => Self::Low,
+        }
+    }
+}
+type Modules<'a> = Vec<Box<dyn Module<'a>>>;
+type PulseResult<'a> = (Pulse, &'a [&'a str]);
+trait Module<'a> {
+    fn pulse(&self, sender: &'a str, input: Pulse) -> PulseResult;
+    fn name(&self) -> &'a str;
+    fn as_any(&self) -> &(dyn Any + 'a);
+}
+struct Broadcaster<'a> {
+    outputs: Vec<&'a str>,
+    name: &'a str,
+}
+impl<'a> Module<'a> for Broadcaster<'a> {
+    fn pulse(&self, _: &str, input: Pulse) -> PulseResult {
+        (input, &self.outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Broadcaster<'a> {
+    fn new(name: &'a str, outputs: Vec<&'a str>) -> Self {
+        Self { name, outputs }
+    }
+}
+struct Dummy<'a> {
+    name: &'a str,
+}
+impl<'a> Module<'a> for Dummy<'a> {
+    fn pulse(&self, _: &str, _input: Pulse) -> PulseResult {
+        (Pulse::Low, &[])
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Dummy<'a> {
+    fn new(name: &'a str) -> Self {
+        Self { name }
+    }
+}
+struct Flipflop<'a> {
+    state: Cell<bool>,
+    outputs: Vec<&'a str>,
+    name: &'a str,
+}
+impl<'a> Module<'a> for Flipflop<'a> {
+    fn pulse(&self, _: &str, input: Pulse) -> PulseResult {
+        if let Pulse::High = input {
+            return (Pulse::Low, &[]);
+        }
+        match self.state.get() {
+            true => self.state.set(false),
+            false => self.state.set(true),
+        }
+        let state = self.state.get().into();
+        (state, &self.outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Flipflop<'a> {
+    fn new(name: &'a str, outputs: Vec<&'a str>) -> Self {
+        Self {
+            name,
+            outputs,
+            state: Cell::new(false),
+        }
+    }
+}
+struct Conjunction<'a> {
+    name: &'a str,
+    inputs: RefCell<HashMap<&'a str, Pulse>>,
+    outputs: Vec<&'a str>,
+}
+impl<'a> Module<'a> for Conjunction<'a> {
+    fn pulse(&self, sender: &'a str, input: Pulse) -> PulseResult {
+        let all_high = {
+            self.inputs.borrow_mut().insert(sender, input);
+            self.inputs.borrow().values().all(|&p| p == Pulse::High)
+            // all high -> low
+            // mixed -> high
+            // all low -> high
+        };
+        let pulse = all_high.not().into();
+        (pulse, &self.outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Conjunction<'a> {
+    fn new(name: &'a str, outputs: Vec<&'a str>, inputs: Vec<&'a str>) -> Self {
+        Self {
+            name,
+            inputs: RefCell::new(HashMap::from_iter(
+                inputs.into_iter().map(|i| (i, Pulse::Low)),
+            )),
+            outputs,
+        }
+    }
+}
+
+fn new_module<'a>(
+    name: &'a str,
+    outputs: Vec<&'a str>,
+    inputs: Vec<&'a str>,
+) -> Box<dyn Module<'a> + 'a> {
+    if name == "broadcaster" {
+        return Box::new(Broadcaster::new(name, outputs));
+    }
+    if name.starts_with('%') {
+        return Box::new(Flipflop::new(name.strip_prefix('%').unwrap(), outputs));
+    }
+    if name.starts_with('&') {
+        return Box::new(Conjunction::new(
+            name.strip_prefix('&').unwrap(),
+            outputs,
+            inputs,
+        ));
+    }
+    return Box::new(Dummy::new(name));
+}
+
+fn parse(input: &'static str) -> Vec<Box<dyn Module<'static> + 'static>> {
+    input
+        .lines()
+        .map(|line| {
+            let mut s = line.split_whitespace();
+            let name = s.next().unwrap().trim();
+
+            let outputs = s
+                .skip(1)
+                .map(|c| c.trim_matches([' ', ','].as_ref()))
+                .collect();
+
+            let inputs = input
+                .lines()
+                .filter_map(|line| {
+                    let s = line.split_once("->").unwrap();
+                    if !s.1.contains(name.trim_matches([' ', '&', '%'].as_ref())) {
+                        return None;
+                    }
+                    Some(s.0.trim_matches([' ', '&', '%'].as_ref()))
+                })
+                .collect();
+            new_module(name, outputs, inputs)
+        })
+        .collect::<Vec<_>>()
+}
+
+fn press_button<'a>(modules: &Modules<'a>) -> (usize, usize) {
+    let mut queue: VecDeque<(&'a str, PulseResult)> = VecDeque::new();
+    let mut counter = (1, 0);
+    let broadcaster = modules.iter().find(|m| m.name() == "broadcaster").unwrap();
+    queue.push_back((broadcaster.name(), broadcaster.pulse("button", Pulse::Low)));
+    while let Some((name, (pulse, outputs))) = queue.pop_front() {
+        for output in outputs {
+            counter = counter + pulse;
+            if let Some(module) = modules.iter().find(|&m| m.name() == *output) {
+                queue.push_back((module.name(), module.pulse(name, pulse)));
+            }
+        }
+    }
+    counter
+}
+
+fn part1(input: &'static str) -> usize {
+    let modules = parse(input);
+    let count = (0..1000)
+        .map(|_| press_button(&modules))
+        .fold((0, 0), |a, b| (a.0 + b.0, a.1 + b.1));
+    count.0 * count.1
+}
+fn part2(input: &str) -> usize {
+    todo!()
+}
+fn main() {
+    let input: &str = include_str!("../input.txt");
+    println!("Part 1: {}", part1(input));
+    println!("Part 2: {}", part2(input));
+}
+
+#[cfg(test)]
+mod tests {
+    const INPUT: &str = "broadcaster -> a, b, c
+%a -> b
+%b -> c
+%c -> inv
+&inv -> a";
+    const INPUT2: &str = "broadcaster -> a
+%a -> inv, con
+&inv -> b
+%b -> con
+&con -> output";
+    #[test]
+    fn part1() {
+        assert_eq!(super::part1(INPUT), 8000 * 4000);
+    }
+    #[test]
+    fn part1_2() {
+        assert_eq!(super::part1(INPUT2), 4250 * 2750);
+    }
+    #[test]
+    fn part2() {
+        assert_eq!(super::part2(INPUT), 0);
+    }
+}
diff --git a/2023/day20/src/recursive_version/main.rs b/2023/day20/src/recursive_version/main.rs
new file mode 100644
index 0000000..53d423c
--- /dev/null
+++ b/2023/day20/src/recursive_version/main.rs
@@ -0,0 +1,295 @@
+use std::{
+    any::Any,
+    cell::{Cell, RefCell},
+    collections::HashMap,
+    iter,
+    ops::Add,
+    rc::Rc,
+};
+
+#[derive(Copy, Clone, Hash, PartialEq, Eq, Debug)]
+enum Pulse {
+    High,
+    Low,
+}
+impl Add<Pulse> for (usize, usize) {
+    type Output = (usize, usize);
+    fn add(self, pulse: Pulse) -> Self::Output {
+        match pulse {
+            Pulse::High => (self.0, self.1 + 1),
+            Pulse::Low => (self.0 + 1, self.1),
+        }
+    }
+}
+impl From<Pulse> for bool {
+    fn from(p: Pulse) -> Self {
+        match p {
+            Pulse::High => true,
+            Pulse::Low => false,
+        }
+    }
+}
+impl From<bool> for Pulse {
+    fn from(b: bool) -> Self {
+        match b {
+            true => Self::High,
+            false => Self::Low,
+        }
+    }
+}
+type Outputs<'a> = Vec<Rc<Box<dyn Module<'a>>>>;
+trait Module<'a> {
+    /// 0 low, 1 high
+    fn pulse(&self, sender: &'a str, input: Pulse) -> (usize, usize);
+    fn connect(&self, output: Outputs<'a>);
+    fn name(&self) -> &'a str;
+    fn as_any(&self) -> &(dyn Any + 'a);
+}
+struct Broadcaster<'a> {
+    outputs: RefCell<Outputs<'a>>,
+    name: &'a str,
+}
+impl<'a> Module<'a> for Broadcaster<'a> {
+    fn pulse(&self, _: &str, input: Pulse) -> (usize, usize) {
+        self.outputs
+            .borrow()
+            .iter()
+            .map(|m| {
+                println!("{} -{input:?}-> {}", self.name, m.name());
+                m.pulse(self.name, input)
+            })
+            .fold((0, 0), |(low, high), (l, h)| (low + l, high + h) + input)
+    }
+    fn connect(&self, outputs: Outputs<'a>) {
+        self.outputs.borrow_mut().extend(outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Broadcaster<'a> {
+    fn new(name: &'a str) -> Self {
+        Self {
+            name,
+            outputs: RefCell::new(Vec::new()),
+        }
+    }
+}
+struct Dummy<'a> {
+    name: &'a str,
+}
+impl<'a> Module<'a> for Dummy<'a> {
+    fn pulse(&self, _: &str, _input: Pulse) -> (usize, usize) {
+        (0, 0)
+    }
+    fn connect(&self, _outputs: Outputs<'a>) {}
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Dummy<'a> {
+    fn new(name: &'a str) -> Self {
+        Self { name }
+    }
+}
+struct Flipflop<'a> {
+    state: Cell<bool>,
+    outputs: RefCell<Outputs<'a>>,
+    name: &'a str,
+}
+impl<'a> Module<'a> for Flipflop<'a> {
+    fn pulse(&self, _: &str, input: Pulse) -> (usize, usize) {
+        if let Pulse::High = input {
+            return (0, 0);
+        }
+        match self.state.get() {
+            true => self.state.set(false),
+            false => self.state.set(true),
+        }
+        let state = self.state.get().into();
+        self.outputs
+            .borrow()
+            .iter()
+            .map(|m| {
+                println!("{} -{state:?}-> {}", self.name, m.name());
+                m.pulse(self.name, state)
+            })
+            .fold((0, 0), |(low, high), (l, h)| (low + l, high + h) + state)
+    }
+    fn connect(&self, outputs: Outputs<'a>) {
+        self.outputs.borrow_mut().extend(outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Flipflop<'a> {
+    fn new(name: &'a str) -> Self {
+        Self {
+            name,
+            state: Cell::new(false),
+            outputs: RefCell::new(Vec::new()),
+        }
+    }
+}
+struct Conjunction<'a> {
+    name: &'a str,
+    inputs: RefCell<HashMap<&'a str, Pulse>>,
+    outputs: RefCell<Outputs<'a>>,
+}
+impl<'a> Module<'a> for Conjunction<'a> {
+    fn pulse(&self, sender: &'a str, input: Pulse) -> (usize, usize) {
+        let pulse = {
+            let mut map = self.inputs.borrow_mut();
+            map.insert(sender, input);
+            map.values().all(|&p| p == Pulse::Low)
+        };
+        let pulse = pulse.into();
+        self.outputs
+            .borrow()
+            .iter()
+            .map(|m| {
+                println!("{} -{pulse:?}-> {}", self.name, m.name());
+                m.pulse(self.name, pulse)
+            })
+            .fold((0, 0), |(low, high), (l, h)| (low + l, high + h) + pulse)
+    }
+    fn connect(&self, outputs: Outputs<'a>) {
+        self.outputs.borrow_mut().extend(outputs)
+    }
+    fn name(&self) -> &'a str {
+        self.name
+    }
+    fn as_any(&self) -> &(dyn Any + 'a) {
+        self
+    }
+}
+impl<'a> Conjunction<'a> {
+    fn new(name: &'a str) -> Self {
+        Self {
+            name,
+            inputs: RefCell::new(HashMap::new()),
+            outputs: RefCell::new(Vec::new()),
+        }
+    }
+    fn populate(&self, inputs: impl Iterator<Item = &'a str>) {
+        let mut map = self.inputs.borrow_mut();
+        for input in inputs {
+            map.insert(input, Pulse::Low);
+        }
+    }
+}
+
+fn new_module<'a>(name: &'a str) -> Box<dyn Module<'a> + 'a> {
+    if name == "broadcaster" {
+        return Box::new(Broadcaster::new(name));
+    }
+    if name.starts_with('%') {
+        return Box::new(Flipflop::new(name.strip_prefix('%').unwrap()));
+    }
+    if name.starts_with('&') {
+        return Box::new(Conjunction::new(name.strip_prefix('&').unwrap()));
+    }
+    return Box::new(Dummy::new(name));
+}
+
+fn parse(input: &'static str) -> Vec<Rc<Box<dyn Module<'static> + 'static>>> {
+    let mut conjunctions = Vec::new();
+
+    let (modules, outputs) = input
+        .lines()
+        .map(|line| {
+            let mut s = line.split_whitespace();
+            let name = s.next().unwrap().trim();
+            let outputs = s
+                .skip(1)
+                .map(|c| c.trim_matches([' ', ','].as_ref()))
+                .collect::<Vec<_>>();
+            let module = Rc::new(new_module(name));
+            if name.starts_with('&') {
+                conjunctions.push(module.clone());
+            }
+            (module, outputs)
+        })
+        .unzip::<_, _, Vec<_>, Vec<_>>();
+
+    for (module, outputs) in modules.iter().zip(outputs) {
+        let outputs_modules = outputs
+            .iter()
+            .map(|&name| {
+                modules
+                    .iter()
+                    .find(|m| m.name() == name)
+                    .cloned()
+                    .unwrap_or_else(|| Rc::new(new_module(name)))
+            })
+            .collect::<Vec<_>>();
+        module.connect(outputs_modules);
+        for con in &conjunctions {
+            if outputs.contains(&con.name()) {
+                println!("adding {} to {} inputs", module.name(), con.name());
+                con.as_any()
+                    .downcast_ref::<Conjunction>()
+                    .unwrap()
+                    .populate(iter::once(module.name()));
+            }
+        }
+    }
+    modules
+}
+
+fn part1(input: &'static str) -> usize {
+    let modules = parse(input);
+    let broadcaster = modules.iter().find(|m| m.name() == "broadcaster").unwrap();
+    let count = (0..4)
+        .map(|_| {
+            println!("button -Low-> broadcaster");
+            broadcaster.pulse("button", Pulse::Low)
+        })
+        .fold((0, 0), |(low, high), (l, h)| (low + l + 1, high + h));
+    dbg!(count);
+    count.0 * count.1
+}
+fn part2(input: &str) -> usize {
+    todo!()
+}
+fn main() {
+    let input: &str = include_str!("../input.txt");
+    println!("Part 1: {}", part1(input));
+    println!("Part 2: {}", part2(input));
+}
+
+#[cfg(test)]
+mod tests {
+    const INPUT: &str = "broadcaster -> a, b, c
+%a -> b
+%b -> c
+%c -> inv
+&inv -> a";
+    const INPUT2: &str = "broadcaster -> a
+%a -> inv, con
+&inv -> b
+%b -> con
+&con -> output";
+    #[test]
+    fn part1() {
+        assert_eq!(super::part1(INPUT), 8000 * 4000);
+    }
+    #[test]
+    fn part1_2() {
+        assert_eq!(super::part1(INPUT2), 4250 * 2750);
+    }
+    #[test]
+    fn part2() {
+        assert_eq!(super::part2(INPUT), 0);
+    }
+}