Day 4

Author: prevostc

README.md

@@ -14,8 +14,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | [Day 1](./src/bin/01.rs) | `66.9µs` | `82.5µs` |
 | [Day 2](./src/bin/02.rs) | `128.2µs` | `224.5µs` |
 | [Day 3](./src/bin/03.rs) | `717.8µs` | `830.1µs` |
+| [Day 4](./src/bin/04.rs) | `810.2µs` | `298.7µs` |
 
-**Total: 2.05ms**
+**Total: 3.16ms**
 <!--- benchmarking table --->
 
 ---

mygrid/src/direction.rs

@@ -14,6 +14,12 @@ pub const DOWN: Direction = Direction::new(1, 0);
 pub const LEFT: Direction = Direction::new(0, -1);
 pub const RIGHT: Direction = Direction::new(0, 1);
 pub const ORTHOGONAL: [Direction; 4] = [UP, DOWN, LEFT, RIGHT];
+pub const DIAGONALS: [Direction; 4] = [
+    UP.add_direction(&RIGHT),
+    RIGHT.add_direction(&DOWN),
+    DOWN.add_direction(&LEFT),
+    LEFT.add_direction(&UP),
+];
 pub const ALL_AROUND: [Direction; 8] = [
     UP,
     UP.add_direction(&RIGHT),
@@ -155,6 +161,15 @@ impl Add<Direction> for Direction {
     }
 }
 
+impl Add<Point> for Direction {
+    type Output = Point;
+
+    #[inline]
+    fn add(self, rhs: Point) -> Self::Output {
+        rhs.apply_direction(self)
+    }
+}
+
 impl Mul<isize> for Direction {
     type Output = Direction;
 

mygrid/src/grid.rs

@@ -24,9 +24,9 @@ impl<T> Grid<T> {
     }
 
     #[inline]
-    pub fn new_from_str(input: &str, map_char: &dyn Fn(char) -> T) -> Self
+    pub fn new_from_str<F>(input: &str, map_char: F) -> Self
     where
-        T: From<char>,
+        F: Fn(char) -> T,
     {
         let width = input.lines().next().unwrap().len();
         let content = input
@@ -196,6 +196,15 @@ impl<T> Grid<T> {
             .enumerate()
             .map(move |(i, t)| (Point::new_usize(i / self.width, i % self.width), t))
     }
+
+    #[inline]
+    pub fn get_item(&self, point: Point) -> Option<&T> {
+        if self.is_in_bounds(point) {
+            Some(&self.content[((point.line as usize) * self.width) + (point.column as usize)])
+        } else {
+            None
+        }
+    }
 }
 
 impl<T> Index<Point> for Grid<T> {
@@ -232,7 +241,7 @@ impl<T> Grid<T> {
     }
 }
 
-impl std::fmt::Display for Grid<String> {
+impl<T: std::fmt::Display> std::fmt::Display for Grid<T> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         for r in 0..self.height {
             for c in 0..self.width {

src/bin/04.rs

@@ -1,11 +1,60 @@
+use mygrid::{
+    direction::{ALL_AROUND, DOWN, LEFT, RIGHT, UP},
+    grid::Grid,
+};
+
 advent_of_code::solution!(4);
 
 pub fn part_one(input: &str) -> Option<u32> {
-    None
+    let grid = Grid::new_from_str(input, |c| c);
+
+    let res = grid
+        .iter_item_and_position()
+        .flat_map(|(point, &c)| ALL_AROUND.iter().map(move |d| (point, c, *d)))
+        .filter(|&(_, c, _)| c == 'X')
+        .filter(|&(point, _, d)| grid.is_in_bounds(point + (d * 3)))
+        .filter(|&(point, _, d)| {
+            let x_pos = point;
+            let m_pos = x_pos + d;
+            let a_pos = m_pos + d;
+            let s_pos = a_pos + d;
+            let spells_xmas = grid[x_pos] == 'X'
+                && grid[m_pos] == 'M'
+                && grid[a_pos] == 'A'
+                && grid[s_pos] == 'S';
+
+            spells_xmas
+        })
+        .count();
+
+    Some(res as u32)
 }
 
 pub fn part_two(input: &str) -> Option<u32> {
-    None
+    let grid = Grid::new_from_str(input, |c| c);
+
+    let res = grid
+        .iter_item_and_position()
+        .filter(|&(_, &c)| c == 'A')
+        .filter(|&(point, _)| {
+            let (Some(&top_left), Some(&top_right), Some(&bot_left), Some(&bot_right)) = (
+                grid.get_item(point + UP + LEFT),
+                grid.get_item(point + UP + RIGHT),
+                grid.get_item(point + DOWN + LEFT),
+                grid.get_item(point + DOWN + RIGHT),
+            ) else {
+                return false;
+            };
+
+            let spells_xmas_diag1 =
+                (top_left == 'M' && bot_right == 'S') || (top_left == 'S' && bot_right == 'M');
+            let spells_xmas_diag2 =
+                (top_right == 'M' && bot_left == 'S') || (top_right == 'S' && bot_left == 'M');
+            spells_xmas_diag1 && spells_xmas_diag2
+        })
+        .count();
+
+    Some(res as u32)
 }
 
 #[cfg(test)]
@@ -15,12 +64,12 @@ mod tests {
     #[test]
     fn test_part_one() {
         let result = part_one(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(18));
     }
 
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(9));
     }
 }