more optimization

2023/day03/src/lib.rs

@@ -1,5 +1,6 @@
-mod p2faster_hash;
 mod p2basic;
+mod p2faster_hash;
+mod p2less_alloc;
 
 use helper::Day;
 
@@ -16,7 +17,8 @@ helper::define_variants! {
     }
     part2 {
         basic => crate::p2basic::part2;
-        fasher_hash => crate::p2faster_hash::part2;
+        faster_hash => crate::p2faster_hash::part2;
+        less_alloc => crate::p2less_alloc::part2;
     }
 }
 
@@ -71,7 +73,6 @@ fn part1(input: &str) -> u64 {
     acc
 }
 
-
 helper::tests! {
     day03 Day03;
     part1 {

2023/day03/src/p2less_alloc.rs

@@ -0,0 +1,109 @@
+use rustc_hash::FxHashMap;
+
+/// States:
+/// - `=0`` -> 0 elements
+/// - `>0, HIGH 0` -> 1 element
+/// - `>0, HIGH 1` -> 2 elements
+/// - `=MAX` -> >2 elements
+#[derive(Debug, Default)]
+struct GearRatio(u64);
+
+const HIGH: u64 = 1 << 63;
+impl GearRatio {
+    fn push(&mut self, value: u64) {
+        if self.0 == 0 {
+            self.0 = value;
+        } else if (self.0 & HIGH) == 0 {
+            self.0 *= value;
+            self.0 |= HIGH;
+        } else {
+            self.0 = u64::MAX;
+        }
+    }
+    fn get(&self) -> Option<u64> {
+        if self.0 > 0 && self.0 != u64::MAX && (self.0 & HIGH) > 1 {
+            Some(self.0 & (HIGH - 1))
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::GearRatio;
+
+    #[test]
+    fn gear_ratio() {
+        let mut r = GearRatio::default();
+        assert_eq!(r.get(), None);
+        r.push(2);
+        assert_eq!(r.get(), None);
+        r.push(3);
+        eprintln!("{:b}", r.0);
+        assert_eq!(r.get(), Some(6));
+        r.push(1);
+        assert_eq!(r.get(), None);
+    }
+}
+
+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, GearRatio> = 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_map(|v| v.get()).sum()
+}