day03, faster hash

2023/day00/src/lib.rs

@@ -37,12 +37,12 @@ fn part2(_input: &str) -> u64 {
 helper::tests! {
     day00 Day00;
     part1 {
-        small => 8;
-        default => 1931;
+        small => 0;
+        default => 0;
     }
     part2 {
-        small => 2286;
-        default => 83105;
+        small => 0;
+        default => 0;
     }
 }
 helper::benchmarks! {}

2023/day03/Cargo.toml

@@ -9,6 +9,7 @@ edition = "2021"
 nom.workspace = true
 helper.workspace = true
 divan.workspace = true
+rustc-hash = "1.1.0"
 
 [[bench]]
 name = "benches"

2023/day03/src/lib.rs

@@ -1,3 +1,5 @@
+mod p2faster_hash;
+
 use std::collections::HashMap;
 
 use helper::Day;
@@ -15,6 +17,7 @@ helper::define_variants! {
     }
     part2 {
         basic => crate::part2;
+        fasher_hash => crate::p2faster_hash::part2;
     }
 }
 

2023/day03/src/p2faster_hash.rs

@@ -0,0 +1,66 @@
+use rustc_hash::FxHashMap;
+
+pub fn part2(input: &str) -> u64 {
+    fn contains_gear(s: &str) -> Option<usize> {
+        s.chars().position(|c| !c.is_ascii_digit() && c != '.')
+    }
+
+    let len = input.lines().next().unwrap().len();
+    let empty_border = std::iter::repeat('.').take(len).collect::<String>();
+
+    let mut prev2 = empty_border.as_str();
+    let mut prev1 = input.lines().next().unwrap();
+
+    let mut gears: FxHashMap<u32, Vec<u64>> = FxHashMap::default();
+
+    for (line_number, next) in input
+        .lines()
+        .skip(1)
+        .chain(Some(empty_border.as_str()))
+        .enumerate()
+    {
+        let mut numbers = prev1.char_indices().peekable();
+        while let Some((start, c)) = numbers.next() {
+            if c.is_ascii_digit() {
+                let mut end = start;
+                while let Some((idx, '0'..='9')) = numbers.next() {
+                    end = idx;
+                }
+
+                let box_bounds = (start.saturating_sub(1))..std::cmp::min(end + 2, len);
+                let number = prev1[start..=end].parse::<u64>().unwrap();
+
+                let mut push = |key: (usize, usize)| {
+                    gears
+                        .entry(((key.1 as u32) << 16) | (key.0 as u32))
+                        .or_default()
+                        .push(number)
+                };
+
+                if let Some(position) = contains_gear(&prev2[box_bounds.clone()]) {
+                    let key = (line_number - 1, box_bounds.start + position);
+                    push(key);
+                }
+
+                if let Some(position) = contains_gear(&prev1[box_bounds.clone()]) {
+                    let key = (line_number, box_bounds.start + position);
+                    push(key);
+                }
+
+                if let Some(position) = contains_gear(&next[box_bounds.clone()]) {
+                    let key = (line_number + 1, box_bounds.start + position);
+                    push(key);
+                }
+            }
+        }
+
+        prev2 = prev1;
+        prev1 = next;
+    }
+
+    gears
+        .values()
+        .filter(|v| v.len() == 2)
+        .map(|v| v[0] * v[1])
+        .sum()
+}