From e45aaad1c470bc03f27377d2887d0c529383b8d2 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Fri, 9 Dec 2022 11:43:33 +0100
Subject: [PATCH] Faster hash set

---
 2022/Cargo.toml      |  1 +
 2022/benches/days.rs | 33 +++++++++++++++------------------
 2022/src/day09.rs    |  9 +++------
 3 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/2022/Cargo.toml b/2022/Cargo.toml
index 9c1cf0d..581f37a 100644
--- a/2022/Cargo.toml
+++ b/2022/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+ahash = "0.8.2"
 anyhow = "1.0.66"
 clap = { version = "4.0.19", features = ["derive"] }
 itertools = "0.10.5"
diff --git a/2022/benches/days.rs b/2022/benches/days.rs
index 500f70b..68dd88d 100644
--- a/2022/benches/days.rs
+++ b/2022/benches/days.rs
@@ -10,34 +10,31 @@ use criterion::Criterion;
 /// Number of days we have an implementation to benchmark
 const DAYS_IMPLEMENTED: u8 = 25;
 
-fn read_input(day: u8) -> Vec<u8> {
+fn read_input(day: u8) -> std::io::Result<Vec<u8>> {
     let input_path = format!("inputs/{:02}.txt", day);
 
     let mut buffer = Vec::new();
-    File::open(input_path)
-        .expect("Failed to open input file")
-        .read_to_end(&mut buffer)
-        .expect("Failed to read input file");
+    File::open(input_path)?.read_to_end(&mut buffer)?;
 
-    buffer
+    Ok(buffer)
 }
 
 pub fn benchmark_days(c: &mut Criterion) {
     for day in 1..=DAYS_IMPLEMENTED {
-        let input = read_input(day);
+        if let Ok(input) = read_input(day) {
+            let part1 = get_implementation(day, false).unwrap();
 
-        let part1 = get_implementation(day, false).unwrap();
-
-        c.bench_with_input(BenchmarkId::new("part1", day), &input, |b, i| {
-            b.iter(|| part1(i));
-        });
-
-        if day < 25 {
-            let part2 = get_implementation(day, true).unwrap();
-
-            c.bench_with_input(BenchmarkId::new("part2", day), &input, |b, i| {
-                b.iter(|| part2(i));
+            c.bench_with_input(BenchmarkId::new("part1", day), &input, |b, i| {
+                b.iter(|| part1(i));
             });
+
+            if day < 25 {
+                let part2 = get_implementation(day, true).unwrap();
+
+                c.bench_with_input(BenchmarkId::new("part2", day), &input, |b, i| {
+                    b.iter(|| part2(i));
+                });
+            }
         }
     }
 }
diff --git a/2022/src/day09.rs b/2022/src/day09.rs
index 48817a1..ed17fac 100644
--- a/2022/src/day09.rs
+++ b/2022/src/day09.rs
@@ -1,9 +1,9 @@
-use std::collections::HashSet;
 use std::ops::Add;
 use std::ops::Index;
 use std::ops::IndexMut;
 use std::ops::Sub;
 
+use ahash::AHashSet;
 use anyhow::Result;
 use nom::bytes::complete::tag;
 use nom::bytes::complete::take;
@@ -101,7 +101,7 @@ fn part_generic<const N: usize>(input: &[u8]) -> Result<String> {
     let mut head_pos = Vec2([0, 0]);
     let mut tails = [head_pos; N];
 
-    let mut visited = HashSet::new();
+    let mut visited = AHashSet::new();
     visited.insert(head_pos);
 
     for (direction, steps) in moves {
@@ -112,7 +112,7 @@ fn part_generic<const N: usize>(input: &[u8]) -> Result<String> {
 
             let mut ref_pos = head_pos;
 
-            for (i, tail_pos) in tails.iter_mut().enumerate() {
+            for tail_pos in &mut tails {
                 let delta = ref_pos - *tail_pos;
 
                 if delta[0].abs() <= 1 && delta[1].abs() <= 1 {
@@ -123,9 +123,6 @@ fn part_generic<const N: usize>(input: &[u8]) -> Result<String> {
 
                 *tail_pos = *tail_pos + step;
 
-                if i == N - 1 {
-                    visited.insert(*tail_pos);
-                }
                 ref_pos = *tail_pos;
             }