1 files changed, 124 insertions, 0 deletions
diff --git a/2021/src/bin/day_2_part_2.rs b/2021/src/bin/day_2_part_2.rs
new file mode 100644
index 0000000..de5b334
--- /dev/null
+++ b/2021/src/bin/day_2_part_2.rs
@@ -0,0 +1,124 @@
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{i64 as nom_i64, line_ending, space1},
+    combinator::map,
+    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)]
+enum Instruction {
+    Forward(Distance),
+    Up(Aim),
+    Down(Aim),
+}
+
+#[derive(
+    Default,
+    Debug,
+    Clone,
+    Copy,
+    derive_more::Add,
+    derive_more::AddAssign,
+    derive_more::Sub,
+    derive_more::SubAssign,
+)]
+struct Distance(i64);
+#[derive(
+    Default,
+    Debug,
+    Clone,
+    Copy,
+    derive_more::Add,
+    derive_more::AddAssign,
+    derive_more::Sub,
+    derive_more::SubAssign,
+)]
+struct Aim(i64);
+
+impl std::ops::Mul<Distance> for Aim {
+    type Output = Distance;
+    fn mul(self, other: Distance) -> Distance {
+        Distance(self.0 * other.0)
+    }
+}
+
+#[derive(Default, Debug)]
+struct Position {
+    horizontal: Distance,
+    depth: Distance,
+    aim: Aim,
+}
+
+impl Position {
+    fn advance(&mut self, instruction: &Instruction) {
+        match instruction {
+            Instruction::Forward(distance) => {
+                self.horizontal += *distance;
+                self.depth += self.aim * *distance;
+            }
+            Instruction::Down(aim) => self.aim += *aim,
+            Instruction::Up(aim) => self.aim -= *aim,
+        }
+    }
+}
+
+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> {
+    alt((parse_forward, parse_up, parse_down))(input)
+}
+
+fn parse_forward(input: &str) -> IResult<&str, Instruction> {
+    map(
+        tuple((tag("forward"), space1, parse_distance)),
+        |(_, _, distance)| Instruction::Forward(distance),
+    )(input)
+}
+fn parse_up(input: &str) -> IResult<&str, Instruction> {
+    map(tuple((tag("up"), space1, parse_aim)), |(_, _, aim)| {
+        Instruction::Up(aim)
+    })(input)
+}
+fn parse_down(input: &str) -> IResult<&str, Instruction> {
+    map(tuple((tag("down"), space1, parse_aim)), |(_, _, aim)| {
+        Instruction::Down(aim)
+    })(input)
+}
+
+fn parse_distance(input: &str) -> IResult<&str, Distance> {
+    map(nom_i64, Distance)(input)
+}
+
+fn parse_aim(input: &str) -> IResult<&str, Aim> {
+    map(nom_i64, Aim)(input)
+}