1 files changed, 100 insertions, 0 deletions
diff --git a/2021/src/bin/day_2.rs b/2021/src/bin/day_2.rs
new file mode 100644
index 0000000..08d01c3
--- /dev/null
+++ b/2021/src/bin/day_2.rs
@@ -0,0 +1,100 @@
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{i64 as nom_i64, line_ending, space1},
+    combinator::{map, value},
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_2.txt")?;
+    let route = parse_route(&input).unwrap().1;
+
+    let mut position = Position::default();
+    for instruction in &route {
+        position.advance(&instruction);
+    }
+    dbg!(position.horizontal.0 * position.depth.0);
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct Route(Vec<Instruction>);
+
+impl<'a> IntoIterator for &'a Route {
+    type Item = &'a Instruction;
+    type IntoIter = std::slice::Iter<'a, Instruction>;
+    fn into_iter(self) -> <Self as IntoIterator>::IntoIter {
+        self.0.iter()
+    }
+}
+
+#[derive(Debug)]
+struct Instruction {
+    direction: Direction,
+    distance: Distance,
+}
+
+#[derive(Debug, Clone)]
+enum Direction {
+    Forward,
+    Up,
+    Down,
+}
+#[derive(
+    Default,
+    Debug,
+    Clone,
+    Copy,
+    derive_more::Add,
+    derive_more::AddAssign,
+    derive_more::Sub,
+    derive_more::SubAssign,
+)]
+struct Distance(i64);
+
+#[derive(Default, Debug)]
+struct Position {
+    horizontal: Distance,
+    depth: Distance,
+}
+
+impl Position {
+    fn advance(&mut self, instruction: &Instruction) {
+        match instruction.direction {
+            Direction::Forward => self.horizontal += instruction.distance,
+            Direction::Down => self.depth += instruction.distance,
+            Direction::Up => self.depth -= instruction.distance,
+        }
+    }
+}
+
+fn parse_route(input: &str) -> IResult<&str, Route> {
+    map(separated_list1(line_ending, parse_instruction), Route)(input)
+}
+
+fn parse_instruction(input: &str) -> IResult<&str, Instruction> {
+    map(
+        tuple((parse_direction, space1, parse_distance)),
+        |(direction, _, distance)| Instruction {
+            direction,
+            distance,
+        },
+    )(input)
+}
+
+fn parse_direction(input: &str) -> IResult<&str, Direction> {
+    alt((
+        value(Direction::Forward, tag("forward")),
+        value(Direction::Up, tag("up")),
+        value(Direction::Down, tag("down")),
+    ))(input)
+}
+
+fn parse_distance(input: &str) -> IResult<&str, Distance> {
+    map(nom_i64, Distance)(input)
+}