added grid utility and used it to speed up day 6

src/day06.rs

@@ -3,6 +3,8 @@ use std::{
     fs::read_to_string,
 };
 
+use crate::utils::grid::Grid;
+
 pub fn day_main() {
     let input = read_to_string("input/day06.txt").unwrap();
     let input = input.trim();
@@ -11,7 +13,7 @@ pub fn day_main() {
 }
 
 type RiddleResult = usize;
-type Point = (i32, i32);
+type Point = (i64, i64);
 
 fn part1(input: &str) -> RiddleResult {
     let (m, pos) = parse(input);
@@ -21,13 +23,9 @@ fn part1(input: &str) -> RiddleResult {
     visited.len()
 }
 
-fn get_visited(
+fn get_visited(m: &Grid<char>, mut pos: Point, mut dir: char) -> HashSet<Point> {
-    m: &HashMap<(i32, i32), char>,
-    mut pos: (i32, i32),
-    mut dir: char,
-) -> HashSet<(i32, i32)> {
     let mut visited = HashSet::new();
-    while m.contains_key(&pos) {
+    while m.contains_key(pos) {
         let (x, y) = pos;
         visited.insert(pos);
         let next = match dir {
@@ -37,7 +35,7 @@ fn get_visited(
             '>' => (x + 1, y),
             _ => unreachable!(),
         };
-        if let Some('#') = m.get(&next) {
+        if m.contains_key(next) && '#' == m[next] {
             dir = match dir {
                 '^' => '>',
                 'v' => '<',
@@ -62,13 +60,13 @@ fn part2(input: &str) -> RiddleResult {
         .count()
 }
 
-fn parse(input: &str) -> (HashMap<Point, char>, Point) {
+fn parse(input: &str) -> (Grid<char>, Point) {
     let mut m = HashMap::new();
     let mut pos = None;
     input.lines().enumerate().for_each(|(y, line)| {
         line.char_indices().for_each(|(x, c)| {
-            let x = x as i32;
+            let x = x as i64;
-            let y = y as i32;
+            let y = y as i64;
             if c == '^' {
                 pos = Some((x, y));
                 m.insert((x, y), '.');
@@ -77,10 +75,10 @@ fn parse(input: &str) -> (HashMap<Point, char>, Point) {
             }
         });
     });
-    (m, pos.unwrap())
+    (Grid::from(m), pos.unwrap())
 }
 
-fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char) -> bool {
+fn is_loop(m: &Grid<char>, block: Point, mut pos: Point, mut dir: char) -> bool {
     let mut visited = HashSet::new();
     loop {
         let (x, y) = pos;
@@ -92,10 +90,9 @@ fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char
             '>' => (x + 1, y),
             _ => unreachable!(),
         };
-        let next_tile = m.get(&next);
+        if !m.contains_key(next) {
-        if None == next_tile {
             return false;
-        } else if next == block || Some(&'#') == next_tile {
+        } else if next == block || '#' == m[next] {
             // we only check for loops on a collision to speed things up
             if visited.contains(&(pos, dir)) {
                 return true;

src/lib.rs

@@ -4,3 +4,4 @@ pub mod day03;
 pub mod day04;
 pub mod day05;
 pub mod day06;
+pub mod utils;

src/utils/grid.rs

@@ -0,0 +1,109 @@
+use std::{
+    collections::HashMap,
+    ops::{Index, IndexMut},
+};
+
+/// A grid structure, indexed by (x, y) tuples. The top-left coordinate is (0, 0).
+pub struct Grid<T> {
+    content_width: i64,
+    content_height: i64,
+    content: Vec<T>,
+}
+
+type Coord = (i64, i64);
+
+impl<T> Grid<T> {
+    pub fn from(mut source: HashMap<Coord, T>) -> Grid<T> {
+        let x_max = source.keys().max_by_key(|c| c.0).unwrap().0;
+        let y_max = source.keys().max_by_key(|c| c.1).unwrap().1;
+        let content_width = x_max + 1;
+        let content_height = y_max + 1;
+        let mut content = Vec::with_capacity((content_width * content_height) as usize);
+        for y in 0..content_height {
+            for x in 0..content_width {
+                let v = source
+                    .remove(&(x, y))
+                    .unwrap_or_else(|| panic!("no entry for {x}, {y}"));
+                content.push(v);
+            }
+        }
+        Grid {
+            content_width,
+            content_height,
+            content,
+        }
+    }
+
+    fn index_of(&self, c: Coord) -> usize {
+        (c.1 * self.content_width + c.0) as usize
+    }
+
+    pub fn get(&self, c: Coord) -> &T {
+        &self.content[self.index_of(c)]
+    }
+    pub fn get_mut(&mut self, c: Coord) -> &mut T {
+        let index_of = self.index_of(c);
+        &mut self.content[index_of]
+    }
+
+    pub fn set(&mut self, c: Coord, value: T) {
+        let index_of = self.index_of(c);
+        self.content[index_of] = value;
+    }
+
+    pub fn contains_key(&self, c: Coord) -> bool {
+        0 <= c.0 && c.0 < self.content_width && 0 <= c.1 && c.1 < self.content_height
+    }
+}
+
+impl<T> Index<Coord> for Grid<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, index: Coord) -> &Self::Output {
+        self.get(index)
+    }
+}
+
+impl<T> IndexMut<Coord> for Grid<T> {
+    fn index_mut(&mut self, index: Coord) -> &mut Self::Output {
+        self.get_mut(index)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::collections::HashMap;
+
+    use super::Grid;
+
+    #[test]
+    fn init_and_read() {
+        let grid: Grid<char> = Grid::from(HashMap::from_iter([
+            ((0, 0), '.'),
+            ((0, 1), '.'),
+            ((1, 0), '.'),
+            ((1, 1), '#'),
+        ]));
+        assert_eq!(&'.', grid.get((0, 0)));
+        assert_eq!(&'.', grid.get((0, 1)));
+        assert_eq!(&'.', grid.get((1, 0)));
+        assert_eq!(&'#', grid.get((1, 1)));
+    }
+    #[test]
+    fn mutate_by_index() {
+        let mut grid = generate();
+        grid[(0, 1)] = 'x';
+        assert_eq!(&'x', grid.get((0, 1)));
+    }
+
+    fn generate() -> Grid<char> {
+        let grid: Grid<char> = Grid::from(HashMap::from_iter([
+            ((0, 0), '.'),
+            ((0, 1), '.'),
+            ((1, 0), '.'),
+            ((1, 1), '.'),
+        ]));
+        grid
+    }
+}

src/utils/mod.rs

@@ -0,0 +1 @@
+pub mod grid;