Day 18 part 2

src/day18.rs

@@ -37,6 +37,35 @@ fn part1(input: &Field) -> usize {
     current.into_iter().flatten().filter(|x| *x).count()
 }
 
+#[aoc(day18, part2)]
+fn part2(input: &Field) -> usize {
+    let mut current = input.clone();
+    let mut next = input.clone();
+    let l = current.len() - 2;
+    for _ in 0..100 {
+        for x in 1..current.len() - 1 {
+            for y in 1..current.len() - 1 {
+                if x == 1 && y == 1 || x == 1 && y == l || x == l && y == 1 || x == l && y == l {
+                    next[x][y] = true;
+                    continue;
+                }
+
+                let now = current[x][y];
+                let neighbors_on: usize = count_neighbors(&current, x, y);
+                let new = if now {
+                    neighbors_on == 2 || neighbors_on == 3
+                } else {
+                    neighbors_on == 3
+                };
+                next[x][y] = new;
+            }
+        }
+        (current, next) = (next, current);
+    }
+    current.into_iter().flatten().filter(|x| *x).count()
+}
+
+
 fn count_neighbors(field: &Field, x: usize, y: usize) -> usize {
     let mut result = 0;
     if field[x - 1][y - 1] {