Implement 2025 - Day 4 - Part 1

2025/04.rs

@@ -0,0 +1,42 @@
+---cargo
+---
+
+static CONTENT: &'static str = include_str!("./inputs/04_1.txt");
+static GRID_OFFSETS: [(isize, isize); 8] = [(-1, -1), (0, -1), (1, -1), (-1, 0), (1, 0), (-1, 1), (0, 1), (1, 1)];
+
+#[derive(Debug, PartialEq, Clone)]
+enum Cell {
+    Empty,
+    PRoll,
+}
+
+fn main() {
+    let grid: Vec<_> = CONTENT.lines().map(|l| l.trim()).filter(|l| !l.is_empty()).map(|l| {
+        l.chars().map(|c| match c {
+            '.' => Cell::Empty,
+            '@' => Cell::PRoll,
+            other => unreachable!("Unexpected Input {:?}", other),
+        }).collect::<Vec<_>>()
+    }).collect();
+
+    let mut result = 0;
+    for (y, row) in grid.iter().enumerate() {
+        for (x, cell) in row.iter().enumerate() {
+            if cell != &Cell::PRoll {
+                continue;
+            }
+
+            let neighbours = GRID_OFFSETS.iter().filter_map(|(xoff, yoff)| Some((x.checked_add_signed(*xoff)?, y.checked_add_signed(*yoff)?))).filter_map(|(x, y)| {
+                let cell = grid.get(y)?.get(x)?;
+                Some((x, y, cell.clone()))
+            }).filter(|(_, _, c)| c == &Cell::PRoll).count();
+    
+
+            if neighbours < 4 {
+                result += 1;
+            }
+        }
+    }
+
+    println!("Result: {}", result);
+}