diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..2f7896d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+target/
diff --git a/day-12/Cargo.lock b/day-12/Cargo.lock
new file mode 100644
index 0000000..b7e1235
--- /dev/null
+++ b/day-12/Cargo.lock
@@ -0,0 +1,78 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-12"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+]
+
+[[package]]
+name = "indoc"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47741a8bc60fb26eb8d6e0238bbb26d8575ff623fdc97b1a2c00c050b9684ed8"
+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce046d161f000fffde5f432a0d034d0341dc152643b2598ed5bfce44c4f3a8f0"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
+name = "proc-macro-hack"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
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+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-xid"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
+name = "unindent"
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diff --git a/day-12/Cargo.toml b/day-12/Cargo.toml
new file mode 100644
index 0000000..35cad43
--- /dev/null
+++ b/day-12/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day-12"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+indoc = "0.3"
diff --git a/day-12/input b/day-12/input
new file mode 100644
index 0000000..bedc29a
--- /dev/null
+++ b/day-12/input
@@ -0,0 +1,771 @@
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diff --git a/day-12/src/main.rs b/day-12/src/main.rs
new file mode 100644
index 0000000..6212c23
--- /dev/null
+++ b/day-12/src/main.rs
@@ -0,0 +1,225 @@
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+ let input = fs::read_to_string("input")?;
+ let actions = parse_actions(&input)?;
+
+ // Part 1
+ let location = simulate_ship_movement(&actions);
+ println!("{}", location.0.abs() + location.1.abs());
+
+ // Part 2
+ let location = simulate_waypoint_movement(&actions);
+ println!("{}", location.0.abs() + location.1.abs());
+
+ Ok(())
+}
+
+#[derive(Copy, Clone, Debug)]
+enum Action {
+ North(u32),
+ South(u32),
+ East(u32),
+ West(u32),
+ Left(u32),
+ Right(u32),
+ Forward(u32),
+}
+
+impl Action {
+ fn new(input: &str) -> Result<Self, String> {
+ if input.len() < 2 {
+ Err(format!("Invalud input line: {}", input))?;
+ }
+
+ let (action, value) = input.split_at(1);
+ let value = value
+ .parse()
+ .map_err(|e| format!("Could not parse value: {}", e))?;
+
+ Ok(match action {
+ "N" => Self::North(value),
+ "S" => Self::South(value),
+ "E" => Self::East(value),
+ "W" => Self::West(value),
+ "L" => Self::Left(value),
+ "R" => Self::Right(value),
+ "F" => Self::Forward(value),
+ _ => Err(format!("Could not parse action: {}", action))?,
+ })
+ }
+
+ fn opposite_direction(self) -> Self {
+ match self {
+ Action::North(x) => Action::South(x),
+ Action::South(x) => Action::North(x),
+ Action::East(x) => Action::West(x),
+ Action::West(x) => Action::East(x),
+ _ => panic!("Invalid direction"),
+ }
+ }
+
+ fn right_direction(self) -> Self {
+ match self {
+ Action::North(x) => Action::East(x),
+ Action::South(x) => Action::West(x),
+ Action::East(x) => Action::South(x),
+ Action::West(x) => Action::North(x),
+ _ => panic!("Invalid direction"),
+ }
+ }
+
+ fn left_direction(self) -> Self {
+ match self {
+ Action::North(x) => Action::West(x),
+ Action::South(x) => Action::East(x),
+ Action::East(x) => Action::North(x),
+ Action::West(x) => Action::South(x),
+ _ => panic!("Invalid direction"),
+ }
+ }
+}
+
+fn parse_actions(input: &str) -> Result<Vec<Action>, String> {
+ input.lines().map(Action::new).collect()
+}
+
+fn simulate_ship_movement(actions: &Vec<Action>) -> (i64, i64) {
+ let mut coords: (i64, i64) = (0, 0);
+ let mut direction = Action::East(0);
+
+ for action in actions {
+ // If the action is Action::Forward, we instead want to move
+ // in a direction determined by our current angle.
+ //
+ // So we convert Action::Forward to a concrete direction.
+
+ let converted_action = if let &Action::Forward(amount) = action {
+ match direction {
+ Action::North(_) => Action::North(amount),
+ Action::South(_) => Action::South(amount),
+ Action::East(_) => Action::East(amount),
+ Action::West(_) => Action::West(amount),
+ _ => unreachable!("Direction can only be NSEW."),
+ }
+ } else {
+ *action
+ };
+
+ match converted_action {
+ Action::North(amount) => {
+ coords.1 += amount as i64;
+ }
+ Action::South(amount) => {
+ coords.1 -= amount as i64;
+ }
+ Action::East(amount) => {
+ coords.0 += amount as i64;
+ }
+ Action::West(amount) => {
+ coords.0 -= amount as i64;
+ }
+ Action::Left(amount) => match amount % 360 {
+ 0 => direction = direction,
+ 90 => direction = direction.left_direction(),
+ 180 => direction = direction.opposite_direction(),
+ 270 => direction = direction.right_direction(),
+ _ => panic!("Only 90 degree turns allowed"),
+ },
+ Action::Right(amount) => match amount % 360 {
+ 0 => direction = direction,
+ 90 => direction = direction.right_direction(),
+ 180 => direction = direction.opposite_direction(),
+ 270 => direction = direction.left_direction(),
+ _ => panic!("Only 90 degree turns allowed"),
+ },
+ Action::Forward(_) => unreachable!("Converted previously"),
+ }
+ }
+
+ coords
+}
+
+fn simulate_waypoint_movement(actions: &Vec<Action>) -> (i64, i64) {
+ let mut waypoint = (1, 10);
+ let mut ship = (0, 0);
+
+ for action in actions {
+ match *action {
+ Action::North(amount) => {
+ waypoint.0 += amount as i64;
+ }
+ Action::South(amount) => {
+ waypoint.0 -= amount as i64;
+ }
+ Action::East(amount) => {
+ waypoint.1 += amount as i64;
+ }
+ Action::West(amount) => {
+ waypoint.1 -= amount as i64;
+ }
+ Action::Left(amount) => match amount % 360 {
+ 0 => {}
+ 90 => waypoint = (waypoint.1, -waypoint.0),
+ 180 => waypoint = (-waypoint.0, -waypoint.1),
+ 270 => waypoint = (-waypoint.1, waypoint.0),
+ _ => panic!("Only 90 degree turns allowed"),
+ },
+ Action::Right(amount) => match amount % 360 {
+ 0 => {}
+ 90 => waypoint = (-waypoint.1, waypoint.0),
+ 180 => waypoint = (-waypoint.0, -waypoint.1),
+ 270 => waypoint = (waypoint.1, -waypoint.0),
+ _ => panic!("Only 90 degree turns allowed"),
+ },
+ Action::Forward(amount) => {
+ ship.0 += waypoint.0 * amount as i64;
+ ship.1 += waypoint.1 * amount as i64;
+ }
+ }
+ }
+
+ ship
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+ use indoc::indoc;
+
+ #[test]
+ fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
+ let input = indoc!(
+ "F10
+ N3
+ F7
+ R90
+ F11
+ "
+ );
+
+ let actions = parse_actions(&input)?;
+ let location = simulate_ship_movement(&actions);
+ assert_eq!(location.0.abs() + location.1.abs(), 25);
+
+ Ok(())
+ }
+
+ #[test]
+ fn test_simple2() -> Result<(), Box<dyn std::error::Error>> {
+ let input = indoc!(
+ "F10
+ N3
+ F7
+ R90
+ F11
+ "
+ );
+
+ let actions = parse_actions(&input)?;
+ let location = simulate_waypoint_movement(&actions);
+ assert_eq!(location.0.abs() + location.1.abs(), 286);
+
+ Ok(())
+ }
+}