Implement 2025 - Day 4 - Part 2

2025/04.rs

@@ -11,7 +11,7 @@ enum Cell {
 }
 
 fn main() {
-    let grid: Vec<_> = CONTENT.lines().map(|l| l.trim()).filter(|l| !l.is_empty()).map(|l| {
+    let mut 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,
@@ -20,6 +20,9 @@ fn main() {
     }).collect();
 
     let mut result = 0;
+
+    loop {
+        let mut to_remove = Vec::new();
         for (y, row) in grid.iter().enumerate() {
             for (x, cell) in row.iter().enumerate() {
                 if cell != &Cell::PRoll {
@@ -34,9 +37,19 @@ fn main() {
 
                 if neighbours < 4 {
                     result += 1;
+                    to_remove.push((x, y));
                 }
             }
         }
+        if to_remove.is_empty() {
+            break;
+        }
+
+        for (x, y) in to_remove {
+            grid[y][x] = Cell::Empty;
+        }
+    }
+
 
     println!("Result: {}", result);
 }