2 files changed, 237 insertions, 4 deletions
diff --git a/2022/Rust/src/day8.rs b/2022/Rust/src/day8.rs
index 6a337f6..3af5d26 100644
--- a/2022/Rust/src/day8.rs
+++ b/2022/Rust/src/day8.rs
@@ -18,7 +18,6 @@ impl Direction {
 }
 
 fn is_visible(grd: &Vec<&str>, direction: &Direction, visible: &mut Vec<Vec<bool>>) {
-    let mut max_height = 0;
     match direction {
         Direction::Up => {
             for j in 0..grd[0].len() {
@@ -109,16 +108,13 @@ fn count_vis_up(pos: (usize, usize), grd: &Vec<&str>) -> usize {
     let mut cnt = 0;
     if is_valid_idx(pos, (grd.len(), grd[0].len()), &Direction::Up) {
         let ch = grd[pos.0].chars().nth(pos.1).unwrap() as u8;
-        // print!("{:?}  ", pos);
         for i in (0..=(pos.0 - 1)).rev() {
-            // print!("{:?}, ", (i, pos.1));
             if grd[i].chars().nth(pos.1).unwrap() as u8 >= ch {
                 cnt += 1;
                 break;
             }
             cnt += 1
         }
-        // println!()
     }
     cnt
 }
diff --git a/2022/Rust/src/day9.rs b/2022/Rust/src/day9.rs
new file mode 100644
index 0000000..b32c910
--- /dev/null
+++ b/2022/Rust/src/day9.rs
@@ -0,0 +1,237 @@
+use std::{collections::HashSet, str::FromStr, string::ParseError};
+
+#[derive(Debug)]
+enum Command {
+    Up(usize),
+    Down(usize),
+    Right(usize),
+    Left(usize),
+}
+
+impl FromStr for Command {
+    type Err = ParseError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (dir, amount) = s.split_once(" ").unwrap();
+        let parsed_amount = amount
+            .parse::<usize>()
+            .expect("Should be parsable to usize");
+        match dir {
+            "R" => Ok(Command::Right(parsed_amount)),
+            "L" => Ok(Command::Left(parsed_amount)),
+            "U" => Ok(Command::Up(parsed_amount)),
+            "D" => Ok(Command::Down(parsed_amount)),
+            _ => unreachable!(),
+        }
+    }
+}
+
+enum Direction {
+    Up,
+    Down,
+    Right,
+    Left,
+    UpRight,
+    UpLeft,
+    DownRight,
+    DownLeft,
+    NoOp,
+}
+
+impl Direction {
+    fn new(diff: (i32, i32)) -> Self {
+        use Direction::*;
+        match diff {
+            (2, 0) => Right,
+            (-2, 0) => Left,
+            (0, 2) => Up,
+            (0, -2) => Down,
+            (1, 2) => UpRight,
+            (2, 1) => UpRight,
+            (2, 2) => UpRight,
+            (-2, 1) => UpLeft,
+            (-1, 2) => UpLeft,
+            (-2, 2) => UpLeft,
+            (-1, -2) => DownLeft,
+            (-2, -2) => DownLeft,
+            (-2, -1) => DownLeft,
+            (2, -1) => DownRight,
+            (2, -2) => DownRight,
+            (1, -2) => DownRight,
+            _ => NoOp,
+        }
+    }
+}
+
+struct Simulation {
+    unique_pos: HashSet<(i32, i32)>, // will mark tail positions
+    head_pos: (i32, i32),
+    tail_pos: Vec<(i32, i32)>,
+}
+
+impl Simulation {
+    fn new(
+        unique_pos: HashSet<(i32, i32)>,
+        head_pos: (i32, i32),
+        tail_pos: Vec<(i32, i32)>,
+    ) -> Self {
+        Simulation {
+            unique_pos,
+            head_pos,
+            tail_pos,
+        }
+    }
+
+    fn update_head(&mut self, command: &Command, tail_idx: usize) {
+        match command {
+            Command::Up(amount) => {
+                for _ in 1..=*amount {
+                    self.head_pos.1 += 1;
+                    for i in 0..9 {
+                        if !self.is_tail_one_block_away(i) {
+                            self.update_tail(&self.get_direction(i), i);
+                            self.unique_pos.insert(self.tail_pos[tail_idx]);
+                        }
+                    }
+                }
+            }
+            Command::Down(amount) => {
+                for _ in 1..=*amount {
+                    self.head_pos.1 -= 1;
+                    for i in 0..9 {
+                        if !self.is_tail_one_block_away(i) {
+                            self.update_tail(&self.get_direction(i), i);
+                            self.unique_pos.insert(self.tail_pos[tail_idx]);
+                        }
+                    }
+                }
+            }
+            Command::Right(amount) => {
+                for _ in 1..=*amount {
+                    self.head_pos.0 += 1;
+                    for i in 0..9 {
+                        if !self.is_tail_one_block_away(i) {
+                            self.update_tail(&self.get_direction(i), i);
+                            self.unique_pos.insert(self.tail_pos[tail_idx]);
+                        }
+                    }
+                }
+            }
+            Command::Left(amount) => {
+                for _ in 1..=*amount {
+                    self.head_pos.0 -= 1;
+                    for i in 0..9 {
+                        if !self.is_tail_one_block_away(i) {
+                            self.update_tail(&self.get_direction(i), i);
+                            self.unique_pos.insert(self.tail_pos[tail_idx]);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn update_tail(&mut self, direction: &Direction, idx: usize) {
+        use Direction::*;
+        match direction {
+            Up => self.tail_pos[idx].1 += 1,
+            Down => self.tail_pos[idx].1 -= 1,
+            Right => self.tail_pos[idx].0 += 1,
+            Left => self.tail_pos[idx].0 -= 1,
+            UpRight => {
+                self.tail_pos[idx].1 += 1;
+                self.tail_pos[idx].0 += 1
+            }
+            UpLeft => {
+                self.tail_pos[idx].1 += 1;
+                self.tail_pos[idx].0 -= 1
+            }
+            DownRight => {
+                self.tail_pos[idx].1 -= 1;
+                self.tail_pos[idx].0 += 1
+            }
+            DownLeft => {
+                self.tail_pos[idx].1 -= 1;
+                self.tail_pos[idx].0 -= 1
+            }
+            NoOp => {}
+        }
+    }
+
+    fn get_pos_diff(&self, idx: usize) -> (i32, i32) {
+        match idx {
+            0 => {
+                let dx = self.head_pos.0 - self.tail_pos[idx].0;
+                let dy = self.head_pos.1 - self.tail_pos[idx].1;
+                (dx, dy)
+            }
+            _ => {
+                let dx = self.tail_pos[idx - 1].0 - self.tail_pos[idx].0;
+                let dy = self.tail_pos[idx - 1].1 - self.tail_pos[idx].1;
+                (dx, dy)
+            }
+        }
+    }
+
+    fn is_tail_one_block_away(&self, idx: usize) -> bool {
+        match idx {
+            0 => {
+                let dx = i32::abs(self.head_pos.0 - self.tail_pos[idx].0);
+                let dy = i32::abs(self.head_pos.1 - self.tail_pos[idx].1);
+                dx + dy + 1 < 3
+            }
+            _ => {
+                let dx = i32::abs(self.tail_pos[idx - 1].0 - self.tail_pos[idx].0);
+                let dy = i32::abs(self.tail_pos[idx - 1].1 - self.tail_pos[idx].1);
+                dx + dy + 1 < 3
+            }
+        }
+    }
+
+    fn get_direction(&self, idx: usize) -> Direction {
+        Direction::new(self.get_pos_diff(idx))
+    }
+}
+
+impl Command {
+    fn apply(&self, simulation: &mut Simulation, tail_idx: usize) {
+        simulation.update_head(self, tail_idx);
+    }
+}
+
+fn solve_part_one(data: &str) -> usize {
+    let tails = vec![(0, 0); 9];
+    let mut simulation = Simulation::new(HashSet::new(), (0, 0), tails);
+    let commands: Vec<_> = data
+        .lines()
+        .map(|x| Command::from_str(x).unwrap())
+        .collect();
+    for command in commands {
+        command.apply(&mut simulation, 0)
+    }
+    simulation.unique_pos.len() + 1
+}
+
+fn solve_part_two(data: &str) -> usize {
+    let tails = vec![(0, 0); 9];
+    let mut simulation = Simulation::new(HashSet::new(), (0, 0), tails);
+    let commands: Vec<_> = data
+        .lines()
+        .map(|x| Command::from_str(x).unwrap())
+        .collect();
+    for command in commands {
+        command.apply(&mut simulation, 8)
+    }
+    simulation.unique_pos.len()
+}
+
+fn main() {
+    let test = include_str!("../input/day9.test");
+    let test_2 = include_str!("../input/day9_2.test");
+    let prod = include_str!("../input/day9.prod");
+    println!("part1 test: {}", solve_part_one(test));
+    println!("part1 test: {}", solve_part_one(test_2));
+    println!("part1 prod: {}", solve_part_one(prod));
+    println!("part2 test: {}", solve_part_two(test));
+    println!("part2 test: {}", solve_part_two(test_2));
+    println!("part2 prod: {}", solve_part_two(prod));
+}