day4: part1

utils/grid/lib.rs

@@ -352,6 +352,28 @@ impl<T: Clone + Eq + PartialEq + Debug> Grid<T> {
         }
     }
 
+    /// Return the count of neighbours (8 directions) matching predicate p
+    pub fn neighbours_count<C: AsCoord2d, P>(&self, c: C, mut p: P) -> usize
+    where
+        P: FnMut(&T) -> bool,
+    {
+        const DIRECTIONS: [(i64, i64); 8] = [
+            (-1, -1),
+            (0, -1),
+            (1, -1),
+            (-1, 0),
+            (1, 0),
+            (1, 1),
+            (0, 1),
+            (-1, 1),
+        ];
+        DIRECTIONS
+            .iter()
+            .map(|d| (c.x() + d.0, c.y() + d.1))
+            .filter(|c| self.get(c).is_some_and(|x| p(x)))
+            .count()
+    }
+
     // fn window_compare_impl<const REV: bool>(&self, needle: &[T]) -> Vec<(i64, i64)> {
     //     if (self.width as usize) < needle.len() {
     //         return Vec::new();