3 files changed, 151 insertions, 1 deletions
diff --git a/2021/rust/Cargo.toml b/2021/rust/Cargo.toml
index 9674b94..8609abe 100644
--- a/2021/rust/Cargo.toml
+++ b/2021/rust/Cargo.toml
@@ -1,7 +1,7 @@
 [workspace]
 members = [
     "day01",
-#    "day02",
+    "day02",
 #    "day03",
 #    "day04",
 #    "day05",
diff --git a/2021/rust/day02/Cargo.toml b/2021/rust/day02/Cargo.toml
new file mode 100644
index 0000000..232d0dc
--- /dev/null
+++ b/2021/rust/day02/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day02"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+aoc = { path = "../../../common/rust/aoc" }
+anyhow = "1.0"
diff --git a/2021/rust/day02/src/main.rs b/2021/rust/day02/src/main.rs
new file mode 100644
index 0000000..4178ecc
--- /dev/null
+++ b/2021/rust/day02/src/main.rs
@@ -0,0 +1,140 @@
+use {
+    anyhow::{
+        anyhow,
+        Context,
+        Result,
+    },
+    std::{
+        env::args,
+        fmt::{
+            Debug,
+            Display,
+        },
+        fs::File,
+        io::{
+            BufRead,
+            BufReader,
+        },
+        path::Path,
+        str::FromStr,
+    },
+};
+
+struct Position {
+    x: isize,
+    y: isize,
+}
+
+impl Display for Position {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "(x: {}, y: {})", self.x, self.y)
+    }
+}
+
+#[derive(PartialEq)]
+enum Command {
+    Down(usize),
+    Forward(usize),
+    Up(usize),
+}
+
+struct CommandError {
+    s: String,
+}
+
+impl CommandError {
+    fn new(s: &str) -> Self {
+        Self {
+            s: String::from(s),
+        }
+    }
+}
+
+type CommandResult<T> = std::result::Result<T, CommandError>;
+
+impl Display for CommandError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "invalid command string: {}", self.s)
+    }
+}
+
+impl Debug for CommandError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "invalid command string: {}", self.s)
+    }
+}
+
+impl FromStr for Command {
+    type Err = CommandError;
+
+    fn from_str(s: &str) -> CommandResult<Self> {
+        let (direction, steps) = s.split_once(' ').ok_or_else(|| CommandError::new(s))?;
+        let count = steps.parse().map_err(|_| CommandError::new(s))?;
+        if direction == "up" {
+            Ok(Command::Up(count))
+        } else if direction == "down" {
+            Ok(Command::Down(count))
+        } else if direction == "forward" {
+            Ok(Command::Forward(count))
+        } else {
+            Err(CommandError::new(s))
+        }
+
+    }
+}
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<Command>> {
+    let reader = BufReader::new(File::open(filename)?);
+
+    reader.lines().map(
+        |v| v?.parse().map_err(|err| anyhow!("Could not parse input: {}", err))
+    ).collect()
+}
+
+fn part1(input: &[Command]) -> Result<Position> {
+    let mut position = Position { x: 0, y:0 };
+    for command in input {
+        match command {
+            Command::Up(steps) => position.y -= *steps as isize,
+            Command::Down(steps) => position.y += *steps as isize,
+            Command::Forward(steps) => position.x += *steps as isize,
+        }
+    }
+
+    Ok(position)
+}
+
+fn part2(input: &[Command]) -> Result<Position> {
+    let mut position = Position { x: 0, y:0 };
+    let mut aim = 0;
+    for command in input {
+        match command {
+            Command::Up(steps) => aim -= *steps as isize,
+            Command::Down(steps) => aim += *steps as isize,
+            Command::Forward(steps) => {
+                position.x += *steps as isize;
+                position.y += aim * *steps as isize;
+            },
+        }
+    }
+
+    Ok(position)
+}
+
+fn main() -> Result<()> {
+    let ( do_part_1, do_part_2 ) = aoc::do_parts();
+
+    let filename = args().nth(1).ok_or(anyhow!("Missing input filename"))?;
+    let input = read_input(filename).context("Could not read input")?;
+    if do_part_1 {
+        let position = part1(&input).context("No solution for part 1")?;
+        let solution = position.x * position.y;
+        println!("Part1, resulting position: {}. Door answer: {}", position, solution);
+    }
+    if do_part_2 {
+        let position = part2(&input).context("No solution for part 1")?;
+        let solution = position.x * position.y;
+        println!("Part2, resulting position: {}. Door answer: {}", position, solution);
+    }
+    Ok(())
+}