day18: perf: swap dijkstra for bfs for ~30% improvement

src/day18.rs

@@ -1,7 +1,7 @@
 use aoc_runner_derive::aoc;
 use grid::Grid;
 use itertools::Itertools;
-use std::{cmp::Reverse, collections::BinaryHeap};
+use std::{cmp::Reverse, collections::{BinaryHeap, VecDeque}};
 
 #[derive(Clone)]
 struct MemoryMap {
@@ -80,6 +80,53 @@ impl MemoryMap {
             .map(|ofs| (pos.0 + ofs.0, pos.1 + ofs.1))
     }
 
+    fn bfs<T: PathTrack>(&self, start: (i64, i64)) -> Option<T> {
+        let goal = (self.map.width() as i64 - 1, self.map.height() as i64 - 1);
+
+        let mut visited = self.map.same_shape(false);
+        let mut prev = self.map.same_shape((i64::MAX, i64::MAX));
+        let mut queue = VecDeque::new();
+
+        visited.set(&start, true);
+        queue.push_back((0, start));
+
+        while let Some((depth, pos)) = queue.pop_front() {
+            if pos == goal {
+                if T::DOES_WORK {
+                    let mut visited_pos = goal;
+                    let mut path = T::new();
+                    path.push(pos);
+                    while let Some(next) = prev.get(&visited_pos) {
+                        visited_pos = *next;
+                        path.push(*next);
+                        if *next == start {
+                            path.finalize();
+                            return Some(path);
+                        }
+                    }
+                } else {
+                    return Some(T::new());
+                }
+            }
+
+            // if visited.get(&pos).is_some_and(|v| *v) {
+            //     continue;
+            // }
+
+            let moves = self.valid_moves(&pos);
+            for new_pos in moves {
+                if visited.get(&new_pos).is_none_or(|v| !v) {
+                    visited.set(&new_pos, true);
+                    if T::DOES_WORK {
+                        prev.set(&new_pos, pos);
+                    }
+                    queue.push_back((depth + 1, new_pos));
+                }
+            }
+        }
+        None
+    }
+
     fn dijkstra<T: PathTrack>(&self, start: (i64, i64)) -> Option<T> {
         let goal = (self.map.width() as i64 - 1, self.map.height() as i64 - 1);
 
@@ -131,7 +178,7 @@ impl MemoryMap {
 pub fn part1_impl(input: &str, width: usize, height: usize, initial_safe_byte_count: usize) -> usize {
     let mut map = MemoryMap::from_str(input, width, height);
     map.place_bytes(0, initial_safe_byte_count - 1);
-    let path = map.dijkstra::<LengthPath>((0, 0)).expect("no path found");
+    let path = map.bfs::<LengthPath>((0, 0)).expect("no path found");
 
     path.0 - 1 // count edges, not visited nodes (start doesn't count)
 }
@@ -141,7 +188,7 @@ pub fn part2_impl_brute(input: &str, width: usize, height: usize, initial_safe_b
     let mut input_map = MemoryMap::from_str(input, width, height);
     input_map.place_bytes(0, initial_safe_byte_count - 1);
 
-    let mut path = input_map.dijkstra::<Vec<(i64, i64)>>((0, 0)).expect("no path found");
+    let mut path = input_map.bfs::<Vec<(i64, i64)>>((0, 0)).expect("no path found");
 
     for byte in initial_safe_byte_count..input_map.byte_stream.len() {
         input_map.place_byte(byte);
@@ -149,7 +196,7 @@ pub fn part2_impl_brute(input: &str, width: usize, height: usize, initial_safe_b
         if let Some((obs_at, _)) = path.iter().find_position(|v| *v == &input_map.byte_stream[byte]) {
             let (before, _) = path.split_at(obs_at);
 
-            if let Some(new_path) = input_map.dijkstra::<Vec<(i64, i64)>>(path[obs_at - 1]) {
+            if let Some(new_path) = input_map.bfs::<Vec<(i64, i64)>>(path[obs_at - 1]) {
                 path = [before, &new_path].concat();
             } else {
                 return input_map.byte_stream[byte];
@@ -172,7 +219,7 @@ pub fn part2_impl(input: &str, width: usize, height: usize, initial_safe_byte_co
         // avoiding this clone by rolling back the byte placements instead is slower
         let mut local_map = input_map.clone();
         local_map.place_bytes(initial_safe_byte_count, *byte);
-        local_map.dijkstra::<NoopTrack>((0, 0)).is_some()
+        local_map.bfs::<NoopTrack>((0, 0)).is_some()
     }) + initial_safe_byte_count;
 
     return input_map.byte_stream[solution];

utils/grid/lib.rs

@@ -1,7 +1,7 @@
 use std::{
     fmt::{Debug, Display, Formatter, Write},
     io::{BufRead, Cursor},
-    iter::repeat,
+    iter::repeat_n,
     mem::swap,
     ops::{Add, AddAssign, Sub},
     str::FromStr,
@@ -82,29 +82,76 @@ where
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
+#[derive(Debug)]
+pub struct GridRowIter<'a, T> {
+    iter: std::slice::Iter<'a, T>,
+}
+
+impl<'a, T: Clone + Eq + PartialEq + Debug> GridRowIter<'a, T> {
+    fn new(grid: &'a Grid<T>, y: i64) -> Self {
+        let iter = grid.data[y as usize * grid.width()..(y as usize + 1) * grid.width()].iter();
+        Self { iter }
+    }
+}
+
+impl<'a, T> Iterator for GridRowIter<'a, T> {
+    type Item = &'a T;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[derive(Debug)]
+pub struct GridColIter<'a, T> {
+    grid: &'a Grid<T>,
+    stride: usize,
+    cur: usize,
+}
+
+impl<'a, T: Clone + Eq + PartialEq + Debug> GridColIter<'a, T> {
+    fn new(grid: &'a Grid<T>, x: i64) -> Self {
+        Self {
+            grid,
+            stride: grid.width(),
+            cur: x as usize,
+        }
+    }
+}
+
+impl<'a, T: Clone + Eq + PartialEq + Debug> Iterator for GridColIter<'a, T> {
+    type Item = &'a T;
+    fn next(&mut self) -> Option<Self::Item> {
+        let cur = self.cur;
+        self.cur += self.stride;
+        if cur < self.grid.data.len() {
+            Some(&self.grid.data[cur])
+        } else {
+            None
+        }
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.grid.height() - 1, Some(self.grid.height() - 1))
+    }
+}
+
+#[derive(Clone, Eq, PartialEq, Debug)]
 pub struct Grid<T> {
     pub data: Vec<T>,
     width: i64,
 }
 
 impl<T: Clone + Eq + PartialEq + Debug> Grid<T> {
-    pub fn new(width: i64) -> Self {
-        Self {
-            data: Vec::new(),
-            width,
-        }
-    }
     /// Returns a new [Grid] with the same shape (width x height) as `self`, filled with `fill`
     pub fn same_shape<NT: Clone + Eq + PartialEq + Debug>(&self, fill: NT) -> Grid<NT> {
-        Grid {
-            data: Vec::from_iter(repeat(fill).take(self.width() * self.height())),
-            width: self.width,
-        }
+        Grid::with_shape(self.width(), self.height(), fill)
     }
+    /// Returns a new [Grid] with the given shape (width x height), filled with `fill`
     pub fn with_shape(width: usize, height: usize, fill: T) -> Self {
         Self {
-            data: Vec::from_iter(repeat(fill).take(width * height)),
+            data: Vec::from_iter(repeat_n(fill, width * height)),
             width: width as i64,
         }
     }
@@ -178,9 +225,25 @@ impl<T: Clone + Eq + PartialEq + Debug> Grid<T> {
         }
     }
 
+    pub fn row_iter(&self, y: i64) -> Option<GridRowIter<T>> {
+        if (y as usize) < self.height() {
+            Some(GridRowIter::new(self, y))
+        } else {
+            None
+        }
+    }
+
     pub fn col(&self, x: i64) -> Option<Vec<&T>> {
-        if x < self.width() as i64 && x >= 0 {
-            Some((0..self.height()).map(|y| self.get(&(x, y as i64)).unwrap()).collect())
+        if let Some(iter) = self.col_iter(x) {
+            Some(iter.collect())
+        } else {
+            None
+        }
+    }
+
+    pub fn col_iter(&self, x: i64) -> Option<GridColIter<T>> {
+        if (x as usize) < self.width() {
+            Some(GridColIter::new(self, x))
         } else {
             None
         }
@@ -350,6 +413,28 @@ FBCG";
         assert_eq!(grid.forward_slice(&(0, 2), 4), Some(b"IJKL".as_slice()));
     }
 
+    #[test]
+    fn row_iter() {
+        let grid = unchecked_load();
+        assert_eq!(
+            grid.row_iter(2).unwrap().collect::<Vec<_>>(),
+            [&b'I', &b'J', &b'K', &b'L']
+        );
+        assert!(grid.row_iter(-1).is_none());
+        assert!(grid.row_iter(4).is_none());
+    }
+
+    #[test]
+    fn col_iter() {
+        let grid = unchecked_load();
+        assert_eq!(
+            grid.col_iter(2).unwrap().collect::<Vec<_>>(),
+            [&b'C', &b'G', &b'K', &b'C']
+        );
+        assert!(grid.col_iter(-1).is_none());
+        assert!(grid.col_iter(4).is_none());
+    }
+
     // #[test]
     // fn window_compare() {
     //     let grid = unchecked_load();