optimize day 11

2023/src/bin/day11.rs

@@ -13,32 +13,32 @@ fn parse_input(raw: &str) -> Parsed {
         .enumerate()
         .flat_map(|(x, l)| l.bytes().enumerate().filter_map(move |(y, b)| (b == b'#').then_some((x, y))))
         .collect_vec();
-    let &xmax = galaxies.iter().map(|(x, _)| x).max().unwrap();
-    let &ymax = galaxies.iter().map(|(_, y)| y).max().unwrap();
-    let mut xs = vec![true; xmax + 1];
-    let mut ys = vec![true; ymax + 1];
+    let max = raw.lines().next().unwrap().len();
+    let mut xs = vec![true; max];
+    let mut ys = vec![true; max];
     for &(x, y) in galaxies.iter() {
         xs[x] = false;
         ys[y] = false;
     }
-    (
-        xs.into_iter().enumerate().filter_map(|(x, b)| b.then_some(x)).collect(),
-        ys.into_iter().enumerate().filter_map(|(y, b)| b.then_some(y)).collect(),
-        galaxies,
-    )
+    (sliding_count(xs), sliding_count(ys), galaxies)
 }
 
-fn distance<const FACTOR: usize>(x1: &I, x2: &I, empty: &[I]) -> I {
-    let smaller_x = x1.min(x2);
-    let bigger_x = x1.max(x2);
-    empty.iter().filter(|x| (smaller_x..=bigger_x).contains(x)).count() * FACTOR + bigger_x - smaller_x
+fn sliding_count(bools: Vec<bool>) -> Vec<I> {
+    bools
+        .into_iter()
+        .scan(0, |prev, b| {
+            *prev += b as I;
+            Some(*prev)
+        })
+        .collect()
 }
 
-fn solve<const FACTOR: usize>((empty_x, empty_y, galaxies): &Parsed) -> usize {
+fn solve<const FACTOR: usize>((x_offset, y_offset, galaxies): &Parsed) -> usize {
     galaxies
         .iter()
+        .map(|&(x, y)| (x + x_offset[x] * FACTOR, y + y_offset[y] * FACTOR))
         .tuple_combinations()
-        .map(|((x1, y1), (x2, y2))| distance::<FACTOR>(x1, x2, empty_x) + distance::<FACTOR>(y1, y2, empty_y))
+        .map(|((x1, y1), (x2, y2))| x1.abs_diff(x2) + y1.abs_diff(y2))
         .sum()
 }
 
@@ -67,5 +67,5 @@ boilerplate! {
     },
     bench1 == 9623138,
     bench2 == 726820169514,
-    bench_parse: |(a, b, c): &Parsed| (a.len(), b.len(), c.len()) => (9, 11, 432),
+    bench_parse: |(a, b, c): &Parsed| (a.len(), b.len(), c.len()) => (140, 140, 432),
 }