Add solution for 2022 day 09 part 2

2022/Cargo.lock

@@ -40,6 +40,10 @@ version = "0.1.0"
 name = "aoc-2022-08"
 version = "0.1.0"
 
+[[package]]
+name = "aoc-2022-09"
+version = "0.1.0"
+
 [[package]]
 name = "either"
 version = "1.8.0"

2022/Cargo.toml

@@ -8,6 +8,7 @@ members = [
     "./day-06",
     "./day-07",
     "./day-08",
+    "./day-09",
 ]
 
 

2022/README.md

@@ -12,7 +12,7 @@
 | 06  |   ✓    |   ✓    | [Rust]   |
 | 07  |   ✓    |   ✓    | [Rust]   |
 | 08  |   ✓    |   ✓    | [Rust]   |
-| 09  |        |        |          |
+| 09  |   ✓    |   ✓    | [Rust]   |
 | 10  |        |        |          |
 | 11  |        |        |          |
 | 12  |        |        |          |

2022/day-09/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "aoc-2022-09"
+version = "0.1.0"
+edition = "2021"
+
+
+[lib]
+test = false
+doctest = false
+
+
+[dependencies]

2022/day-09/Justfile

@@ -0,0 +1,5 @@
+@part PART INPUT_FILE="inputs/puzzle.txt":
+    cargo --quiet run --bin part_{{PART}} -- {{INPUT_FILE}}
+
+clean:
+    cargo clean

2022/day-09/inputs/test.txt

@@ -0,0 +1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2

2022/day-09/inputs/test2.txt

@@ -0,0 +1,8 @@
+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20

2022/day-09/src/bin/part_one.rs

@@ -0,0 +1,44 @@
+use std::{env, io};
+
+use aoc_2022_09::{parse_input, Rope, Visited};
+
+fn main() -> io::Result<()> {
+    let infile_path = env::args().nth(1).expect("input file");
+
+    let result = solve(&infile_path)?;
+
+    println!("{result}");
+
+    Ok(())
+}
+
+fn solve(path: &str) -> io::Result<usize> {
+    let instructions = parse_input(path)?;
+    let mut rope = Rope::new(2);
+    let mut tail_visited = Visited::new();
+
+    tail_visited.insert(rope.tail().unwrap().clone());
+
+    for instruction in instructions {
+        instruction.apply_to_rope(&mut rope, &mut tail_visited);
+    }
+
+    Ok(tail_visited.len())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn sample() {
+        let result = solve("inputs/test.txt").unwrap();
+        assert_eq!(13, result);
+    }
+
+    #[test]
+    fn puzzle() {
+        let result = solve("inputs/puzzle.txt").unwrap();
+        assert_eq!(6026, result);
+    }
+}

2022/day-09/src/bin/part_two.rs

@@ -0,0 +1,47 @@
+use std::{env, io};
+
+use aoc_2022_09::{parse_input, Rope, Visited};
+
+fn main() -> io::Result<()> {
+    let infile_path = env::args().nth(1).expect("input file");
+
+    let result = solve(&infile_path)?;
+
+    println!("{result}");
+
+    Ok(())
+}
+
+fn solve(path: &str) -> io::Result<usize> {
+    let instructions = parse_input(path)?;
+    let mut rope = Rope::new(10);
+    let mut tail_visited = Visited::new();
+
+    tail_visited.insert(rope.tail().unwrap().clone());
+
+    for instruction in instructions {
+        instruction.apply_to_rope(&mut rope, &mut tail_visited);
+    }
+
+    Ok(tail_visited.len())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn sample() {
+        let result = solve("inputs/test.txt").unwrap();
+        assert_eq!(1, result);
+
+        let result = solve("inputs/test2.txt").unwrap();
+        assert_eq!(36, result);
+    }
+
+    #[test]
+    fn puzzle() {
+        let result = solve("inputs/puzzle.txt").unwrap();
+        assert_eq!(2273, result);
+    }
+}

2022/day-09/src/lib.rs

@@ -0,0 +1,144 @@
+use std::{
+    collections::HashSet,
+    fs::File,
+    io::{self, BufRead, BufReader},
+    path::Path,
+    str::FromStr,
+};
+
+pub type Visited = HashSet<Knot>;
+
+#[derive(Debug)]
+pub struct Rope(Vec<Knot>);
+
+impl Rope {
+    pub fn new(len: usize) -> Self {
+        Self(vec![Knot::default(); len])
+    }
+
+    pub fn move_head(&mut self, change: (isize, isize)) {
+        let mut knots = self.0.iter_mut();
+
+        let mut next_a = knots.next();
+
+        next_a.as_mut().map(|head_knot| {
+            head_knot.0 += change.0;
+            head_knot.1 += change.1;
+        });
+
+        let mut next_b = knots.next();
+
+        loop {
+            if next_a.is_some() && next_b.is_some() {
+                next_a.as_mut().map(|knot_a| {
+                    next_b.as_mut().map(|knot_b| {
+                        knot_b.follow(&knot_a);
+                    });
+                });
+
+                next_a = next_b;
+                next_b = knots.next();
+            } else {
+                break;
+            }
+        }
+    }
+
+    pub fn tail(&self) -> Option<&Knot> {
+        self.0.last()
+    }
+}
+
+#[derive(Debug, Default, Clone, PartialEq, Eq, Hash)]
+pub struct Knot(isize, isize);
+
+impl Knot {
+    pub fn follow(&mut self, other: &Self) {
+        let dx = other.0 - self.0;
+        let dxa = dx.abs();
+        let dy = other.1 - self.1;
+        let dya = dy.abs();
+        let same_row = self.0 == other.0;
+        let same_col = self.1 == other.1;
+
+        let x = if dx.is_negative() { -1 } else { 1 };
+        let y = if dy.is_negative() { -1 } else { 1 };
+
+        if (!same_row && !same_col) && (dxa > 1 || dya > 1) {
+            self.0 += x;
+            self.1 += y;
+        } else if dxa > 1 {
+            self.0 += x;
+        } else if dya > 1 {
+            self.1 += y;
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum Instruction {
+    Up(isize),
+    Right(isize),
+    Left(isize),
+    Down(isize),
+}
+
+impl FromStr for Instruction {
+    type Err = String;
+
+    fn from_str(val: &str) -> Result<Self, Self::Err> {
+        let parts = val.split_whitespace().collect::<Vec<&str>>();
+        let [direction, distance, ..] = parts[..] else {
+            return Err("Invalid instruction".to_string());
+        };
+        let distance = distance
+            .parse()
+            .map_err(|_| "Invalid distance value".to_string())?;
+
+        let result = match direction {
+            "U" => Self::Up(distance),
+            "R" => Self::Right(distance),
+            "L" => Self::Left(distance),
+            "D" => Self::Down(distance),
+            _ => return Err("Invalid direction value".to_string()),
+        };
+
+        Ok(result)
+    }
+}
+
+impl Instruction {
+    pub fn apply_to_rope(&self, rope: &mut Rope, tail_visited: &mut Visited) {
+        let (change, amount) = match *self {
+            Instruction::Up(dist) => ((1, 0), dist),
+            Instruction::Right(dist) => ((0, 1), dist),
+            Instruction::Left(dist) => ((0, -1), dist),
+            Instruction::Down(dist) => ((-1, 0), dist),
+        };
+
+        for _ in 0..amount {
+            let old_tail = rope.tail().unwrap().clone();
+
+            rope.move_head(change);
+
+            let new_tail = rope.tail().unwrap();
+
+            if old_tail != *new_tail {
+                tail_visited.insert(new_tail.clone());
+            }
+        }
+    }
+}
+
+pub fn parse_input<P>(path: P) -> io::Result<Vec<Instruction>>
+where
+    P: AsRef<Path>,
+{
+    let file = File::open(path)?;
+    let instructions = BufReader::new(file)
+        .lines()
+        .map(|line| line.unwrap().parse().unwrap())
+        .collect();
+
+    Ok(instructions)
+}

README.md

@@ -9,4 +9,4 @@
 -   [2019](2019/README.md) (0% completed)
 -   [2020](2020/README.md) (20% completed)
 -   [2021](2021/README.md) (68% completed)
--   [2022](2022/README.md) (32% completed)
+-   [2022](2022/README.md) (36% completed)