Add day 2 solution

day2/Cargo.lock

@@ -0,0 +1,39 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day2"
+version = "0.1.0"
+dependencies = [
+ "nom",
+]
+
+[[package]]
+name = "memchr"
+version = "2.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "308cc39be01b73d0d18f82a0e7b2a3df85245f84af96fdddc5d202d27e47b86a"
+
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b1d11e1ef389c76fe5b81bcaf2ea32cf88b62bc494e19f493d0b30e7a930109"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+ "version_check",
+]
+
+[[package]]
+name = "version_check"
+version = "0.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5fecdca9a5291cc2b8dcf7dc02453fee791a280f3743cb0905f8822ae463b3fe"

day2/Cargo.toml

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+[package]
+name = "day2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "7.1"

day2/src/main.rs

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+#![warn(clippy::all, clippy::pedantic)]
+
+use nom::{
+    branch::alt,
+    bytes::complete::{tag, take_while1},
+    character::is_digit,
+    combinator::{eof, map_res},
+    sequence::{separated_pair, terminated},
+    IResult,
+};
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+enum Part {
+    Part1,
+    Part2,
+}
+
+/// The direction of a sub command
+enum Direction {
+    Forward(i32),
+    Down(i32),
+    Up(i32),
+}
+
+/// The location of the sub
+#[derive(Default)]
+struct Location {
+    position: i32,
+    depth: i32,
+    aim: i32,
+}
+
+impl Location {
+    /// Produce a new location that is moved based  based on simple directionality:
+    /// forward/up/down map to positions and depths
+    fn perform_directional_move(&self, direction: &Direction) -> Location {
+        match direction {
+            Direction::Up(n) => Location {
+                position: self.position,
+                depth: self.depth - n,
+                aim: self.aim,
+            },
+            Direction::Down(n) => Location {
+                position: self.position,
+                depth: self.depth + n,
+                aim: self.aim,
+            },
+            Direction::Forward(n) => Location {
+                position: self.position + n,
+                depth: self.depth,
+                aim: self.aim,
+            },
+        }
+    }
+
+    /// Produce a new location that is moved based on the current aim; depth is controlled by a multiple of aim
+    fn perform_aim_based_move(&self, direction: &Direction) -> Location {
+        match direction {
+            Direction::Up(n) => Location {
+                position: self.position,
+                depth: self.depth,
+                aim: self.aim - n,
+            },
+            Direction::Down(n) => Location {
+                position: self.position,
+                depth: self.depth,
+                aim: self.aim + n,
+            },
+            Direction::Forward(n) => Location {
+                position: self.position + n,
+                depth: self.depth + (self.aim * n),
+                aim: self.aim,
+            },
+        }
+    }
+}
+
+fn simulate(directions: &[Direction], part: &Part) -> i32 {
+    let final_location =
+        directions
+            .iter()
+            .fold(Location::default(), |memo, direction| match part {
+                Part::Part1 => memo.perform_directional_move(direction),
+                Part::Part2 => memo.perform_aim_based_move(direction),
+            });
+
+    final_location.position * final_location.depth
+}
+
+fn parse_line(line: &str) -> IResult<&str, Direction> {
+    let parse_direction = alt((tag("forward"), tag("down"), tag("up")));
+    let (_, (raw_direction, magnitude)) = terminated(
+        separated_pair(
+            parse_direction,
+            tag(" "),
+            map_res(take_while1(|c| is_digit(c as u8)), str::parse),
+        ),
+        eof,
+    )(line)?;
+
+    let direction = match raw_direction {
+        "forward" => Direction::Forward,
+        "down" => Direction::Down,
+        "up" => Direction::Up,
+        _ => panic!("invalid direction returned by parser; this can't happen"),
+    }(magnitude);
+
+    Ok(("", direction))
+}
+
+fn main() {
+    let input_file_name = env::args().nth(1).expect("No input filename specified");
+    let input_file = File::open(input_file_name).expect("Could not open input file");
+    let lines = BufReader::new(input_file)
+        .lines()
+        .map(|res| res.expect("Failed to read line"))
+        .collect::<Vec<_>>();
+
+    let directions = lines
+        .iter()
+        .map(|line| {
+            parse_line(line)
+                .unwrap_or_else(|err| panic!("Failed to parse line '{}': {}", line, err))
+        })
+        .map(|(_, direction)| direction)
+        .collect::<Vec<_>>();
+
+    println!("Part 1: {}", simulate(&directions, &Part::Part1));
+    println!("Part 2: {}", simulate(&directions, &Part::Part2));
+}