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2023/day03/src/lib.rs

@@ -1,6 +1,7 @@
 mod p2basic;
 mod p2faster_hash;
 mod p2less_alloc;
+mod p2less_with_capacity;
 
 use helper::Day;
 
@@ -18,6 +19,7 @@ helper::define_variants! {
     part2 {
         basic => crate::p2basic::part2;
         faster_hash => crate::p2faster_hash::part2;
+        p2less_with_capacity => crate::p2less_with_capacity::part2;
         less_alloc => crate::p2less_alloc::part2;
     }
 }

2023/day03/src/p2less_alloc.rs

@@ -1,3 +1,5 @@
+use std::hash::BuildHasherDefault;
+
 use rustc_hash::FxHashMap;
 
 /// States:
@@ -58,7 +60,8 @@ pub fn part2(input: &str) -> u64 {
     let mut prev2 = empty_border.as_str();
     let mut prev1 = input.lines().next().unwrap();
 
-    let mut gears: FxHashMap<u32, GearRatio> = FxHashMap::default();
+    let mut gears: FxHashMap<u32, GearRatio> =
+        FxHashMap::with_capacity_and_hasher(1000, BuildHasherDefault::default());
 
     for (line_number, next) in input
         .lines()

2023/day03/src/p2less_with_capacity.rs

@@ -0,0 +1,69 @@
+use std::hash::BuildHasherDefault;
+
+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::with_capacity_and_hasher(1000, BuildHasherDefault::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()
+}