2022 day9/rust: abort early if knot doesn't move

2022/day9/rust/src/main.rs

@@ -1,3 +1,4 @@
+#![feature(iterator_try_reduce)]
 #![warn(clippy::pedantic)]
 
 use std::{
@@ -7,15 +8,14 @@ use std::{
 
 use aoc::vec2::{Direction, Vec2};
 
-fn tail_movement(following: Vec2, tail: Vec2) -> Vec2 {
-    let (dx, dy) = (following - tail).into();
+fn knot_movement(previous: Vec2, knot: Vec2) -> Option<Vec2> {
+    let (dx, dy) = (previous - knot).into();
 
-    let movement = if dx.abs() <= 1 && dy.abs() <= 1 {
-        (0, 0)
+    if dx.abs() <= 1 && dy.abs() <= 1 {
+        None
     } else {
-        (dx.signum(), dy.signum())
-    };
-    movement.into()
+        Some((dx.signum(), dy.signum()).into())
+    }
 }
 
 fn simulate_knots(num_knots: usize, instructions: &[(Direction, usize)]) -> usize {
@@ -31,15 +31,12 @@ fn simulate_knots(num_knots: usize, instructions: &[(Direction, usize)]) -> usiz
         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);
+            if let Some(tail) = knots.iter_mut().try_reduce(|previous, knot| {
+                *knot += knot_movement(*previous, *knot)?;
+                Some(knot)
+            }) {
+                tail_positions.insert(tail.copied().unwrap());
+            }
         }
     }
 

common/rust/src/vec2.rs

@@ -1,5 +1,6 @@
 use std::{
-    ops::{Add, AddAssign, Sub, SubAssign},
+    fmt,
+    ops::{Add, AddAssign, Mul, Sub, SubAssign},
     str::FromStr,
 };
 
@@ -22,6 +23,17 @@ impl Vec2 {
             y: f(self.y),
         }
     }
+
+    #[must_use]
+    pub fn len(self) -> f64 {
+        (f64::from(self.x).powi(2) + f64::from(self.y).powi(2)).sqrt()
+    }
+}
+
+impl fmt::Display for Vec2 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", (self.x, self.y))
+    }
 }
 
 impl Add for Vec2 {
@@ -60,6 +72,28 @@ impl SubAssign for Vec2 {
     }
 }
 
+impl Mul<i32> for Vec2 {
+    type Output = Self;
+
+    fn mul(self, n: i32) -> Self::Output {
+        Vec2 {
+            x: self.x * n,
+            y: self.y * n,
+        }
+    }
+}
+
+impl Mul<Vec2> for i32 {
+    type Output = Vec2;
+
+    fn mul(self, Vec2 { x, y }: Vec2) -> Self::Output {
+        Vec2 {
+            x: x * self,
+            y: y * self,
+        }
+    }
+}
+
 impl From<(i32, i32)> for Vec2 {
     fn from((x, y): (i32, i32)) -> Self {
         Self { x, y }