2022 day9/rust: cleanup

2022/day9/rust/src/main.rs

@@ -3,113 +3,63 @@
 use std::{
     collections::BTreeSet,
     io::{stdin, Read},
-    ops::{Add, AddAssign, Sub},
 };
 
-use aoc::*;
+use aoc::vec2::{Direction, Vec2};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct Vec2 {
-    x: i32, // increases toward right
-    y: i32, // increases toward top
+fn tail_movement(following: Vec2, tail: Vec2) -> Vec2 {
+    let (dx, dy) = (following - tail).into();
+
+    let movement = if dx.abs() <= 1 && dy.abs() <= 1 {
+        (0, 0)
+    } else {
+        (dx.signum(), dy.signum())
+    };
+    movement.into()
 }
 
-impl Vec2 {
-    #[must_use]
-    pub fn new(x: i32, y: i32) -> Self {
-        Self { x, y }
+fn simulate_knots(num_knots: usize, instructions: &[(Direction, usize)]) -> usize {
+    const START: Vec2 = Vec2::new(0, 0);
+
+    assert!(num_knots >= 2);
+
+    let mut knots = vec![START; num_knots];
+    let mut tail_positions = BTreeSet::new();
+    tail_positions.insert(START);
+
+    for (direction, distance) in instructions {
+        for _i in 0..*distance {
+            knots[0] += Vec2::from(*direction);
+
+            let tail = knots
+                .iter_mut()
+                .reduce(|following, knot| {
+                    *knot += tail_movement(*following, *knot);
+                    knot
+                })
+                .unwrap();
+
+            tail_positions.insert(*tail);
+        }
     }
 
-    #[must_use]
-    pub fn map(self, mut f: impl FnMut(i32) -> i32) -> Self {
-        Self {
-            x: f(self.x),
-            y: f(self.y),
-        }
-    }
-}
-
-impl Add for Vec2 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self::Output {
-        Self {
-            x: self.x + rhs.x,
-            y: self.y + rhs.y,
-        }
-    }
-}
-
-impl AddAssign for Vec2 {
-    fn add_assign(&mut self, rhs: Self) {
-        self.x += rhs.x;
-        self.y += rhs.y;
-    }
-}
-
-impl Sub for Vec2 {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self::Output {
-        Self {
-            x: self.x - rhs.x,
-            y: self.y - rhs.y,
-        }
-    }
-}
-
-impl From<(i32, i32)> for Vec2 {
-    fn from((x, y): (i32, i32)) -> Self {
-        Self { x, y }
-    }
-}
-
-impl From<Vec2> for (i32, i32) {
-    fn from(v: Vec2) -> Self {
-        (v.x, v.y)
-    }
-}
-
-fn get_direction_vec(direction: &str) -> Vec2 {
-    match direction {
-        "U" => (0, 1),
-        "R" => (1, 0),
-        "D" => (0, -1),
-        "L" => (-1, 0),
-        _ => panic!(),
-    }
-    .into()
+    tail_positions.len()
 }
 
 fn main() {
     let mut data = String::new();
     stdin().read_to_string(&mut data).unwrap();
 
-    let mut knots = vec![Vec2::new(0, 0); 10];
-
-    let mut tail_positions = BTreeSet::new();
-    tail_positions.insert(*knots.last().unwrap());
-
-    for line in data.lines() {
+    let instructions: Vec<_> = data
+        .lines()
+        .map(|line| {
             let (direction, distance) = line.split_once(' ').unwrap();
-        let distance: usize = distance.parse().unwrap();
+            let direction = direction.parse().unwrap();
+            let distance = distance.parse().unwrap();
+            (direction, distance)
+        })
+        .collect();
 
-        for _i in 0..distance {
-            knots[0] += get_direction_vec(direction);
-            let mut following = knots[0];
-
-            for knot in &mut knots[1..] {
-                let delta = match (following - *knot).into() {
-                    (x, y) if x.abs() <= 1 && y.abs() <= 1 => (0, 0),
-                    (x, y) => (x.signum(), y.signum()),
-                }
-                .into();
-                *knot += delta;
-                following = *knot;
-            }
-            tail_positions.insert(*knots.last().unwrap());
-        }
-    }
-
-    println!("{:?}", tail_positions.len());
+    println!("{:?}", simulate_knots(2, &instructions));
+    println!("{:?}", simulate_knots(10, &instructions));
 }

common/rust/src/lib.rs

@@ -1,6 +1,7 @@
 #![warn(clippy::pedantic)]
 
 mod section_range;
+pub mod vec2;
 
 use std::{mem, path::Path};
 

common/rust/src/vec2.rs

@@ -0,0 +1,108 @@
+use std::{
+    ops::{Add, AddAssign, Sub, SubAssign},
+    str::FromStr,
+};
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Vec2 {
+    x: i32, // increases toward right
+    y: i32, // increases toward top
+}
+
+impl Vec2 {
+    #[must_use]
+    pub const fn new(x: i32, y: i32) -> Self {
+        Self { x, y }
+    }
+
+    #[must_use]
+    pub fn map(self, mut f: impl FnMut(i32) -> i32) -> Self {
+        Self {
+            x: f(self.x),
+            y: f(self.y),
+        }
+    }
+}
+
+impl Add for Vec2 {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self {
+            x: self.x + rhs.x,
+            y: self.y + rhs.y,
+        }
+    }
+}
+
+impl AddAssign for Vec2 {
+    fn add_assign(&mut self, rhs: Self) {
+        self.x += rhs.x;
+        self.y += rhs.y;
+    }
+}
+
+impl Sub for Vec2 {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self {
+            x: self.x - rhs.x,
+            y: self.y - rhs.y,
+        }
+    }
+}
+
+impl SubAssign for Vec2 {
+    fn sub_assign(&mut self, rhs: Self) {
+        self.x -= rhs.x;
+        self.y -= rhs.y;
+    }
+}
+
+impl From<(i32, i32)> for Vec2 {
+    fn from((x, y): (i32, i32)) -> Self {
+        Self { x, y }
+    }
+}
+
+impl From<Vec2> for (i32, i32) {
+    fn from(v: Vec2) -> Self {
+        (v.x, v.y)
+    }
+}
+
+impl From<Direction> for Vec2 {
+    /// Creates a unit vector in the given direction.
+    fn from(dir: Direction) -> Self {
+        match dir {
+            Direction::Up => (0, 1),
+            Direction::Down => (0, -1),
+            Direction::Left => (-1, 0),
+            Direction::Right => (1, 0),
+        }
+        .into()
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+impl FromStr for Direction {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "U" => Ok(Direction::Up),
+            "D" => Ok(Direction::Down),
+            "L" => Ok(Direction::Left),
+            "R" => Ok(Direction::Right),
+            _ => Err(()),
+        }
+    }
+}