From daad18c6af28c2a944490c10bcff9cba7a031de8 Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Fri, 9 Dec 2022 21:36:05 +0100
Subject: [PATCH] 2022 day9/rust: abort early if knot doesn't move

---
 2022/day9/rust/src/main.rs | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/2022/day9/rust/src/main.rs b/2022/day9/rust/src/main.rs
index 5d4273d..4df0d05 100644
--- a/2022/day9/rust/src/main.rs
+++ b/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 knot_movement(previous: Vec2, knot: Vec2) -> Vec2 {
+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(|previous, knot| {
-                    *knot += knot_movement(*previous, *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());
+            }
         }
     }