Parallelize day 6 part 2 (~83.2% improvement)

Author: UnderscoreTud

Cargo.lock

@@ -29,4 +29,5 @@ tinyjson = "2.5.1"
 
 # Solution dependencies
 itertools = "0.13.0"
+pariter = "0.5.1"
 regex = "1.11.1"

Cargo.toml

@@ -20,16 +20,16 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 <!--- benchmarking table --->
 ## Benchmarks
 
-|                   Day                   | Part 1 | Part 2 |
-|:---------------------------------------:| :---: | :---:  |
-|        [Day 1](./src/bin/01.rs)         | `61.4µs` | `106.8µs` |
-|        [Day 2](./src/bin/02.rs)         | `220.6µs` | `404.8µs` |
-|        [Day 3](./src/bin/03.rs)         | `561.0µs` | `565.5µs` |
-|        [Day 4](./src/bin/04.rs)         | `560.8µs` | `161.9µs` |
-|        [Day 5](./src/bin/05.rs)         | `344.6µs` | `323.6µs` |
-| [Day 6](./src/bin/06.rs) (unoptimized)  | `494.4µs` | `956.4ms` |
-
-**Total: 960.21ms**
+| Day | Part 1 | Part 2 |
+| :---: | :---: | :---:  |
+| [Day 1](./src/bin/01.rs) | `61.4µs` | `106.8µs` |
+| [Day 2](./src/bin/02.rs) | `220.6µs` | `404.8µs` |
+| [Day 3](./src/bin/03.rs) | `561.0µs` | `565.5µs` |
+| [Day 4](./src/bin/04.rs) | `560.8µs` | `161.9µs` |
+| [Day 5](./src/bin/05.rs) | `344.6µs` | `323.6µs` |
+| [Day 6](./src/bin/06.rs) | `499.6µs` | `160.3ms` |
+
+**Total: 164.11ms**
 <!--- benchmarking table --->
 
 ---

README.md

@@ -1,5 +1,6 @@
 use std::collections::HashSet;
 use itertools::Itertools;
+use pariter::{scope, IteratorExt};
 
 advent_of_code::solution!(6);
 
@@ -107,20 +108,22 @@ pub fn part_one(input: &str) -> Option<u32> {
 }
 
 pub fn part_two(input: &str) -> Option<u32> {
-    let mut obstructions = 0;
     let mut map = Map::parse(input);
     map.predict_path();
     let mut original_path = map.visited_pos;
     original_path.remove(&map.starting_pos);
-    for pos in original_path {
-        map.obstacles.insert(pos); 
-        map.visited_pos = HashSet::new();
-        if map.has_loop() {
-            obstructions += 1;
-        }
-        map.obstacles.remove(&pos);
-    }
-    Some(obstructions)
+    Some(scope(|scope| original_path.iter()
+        .parallel_filter_scoped(scope, move |pos| {
+            let mut new_obstacles = map.obstacles.clone();
+            new_obstacles.insert(**pos);
+            let mut map = Map {
+                obstacles: new_obstacles,
+                visited_pos: HashSet::new(),
+                ..map
+            };
+            map.has_loop()
+        })
+        .count() as u32).unwrap())
 }
 
 #[cfg(test)]