1 files changed, 38 insertions, 0 deletions
diff --git a/18/solution.py b/18/solution.py
new file mode 100644
index 0000000..18f378a
--- /dev/null
+++ b/18/solution.py
@@ -0,0 +1,38 @@
+from collections import defaultdict
+
+State = set[tuple[int, int]]
+
+def step(state: State) -> State:
+    def next_cell_state(x: int, y: int) -> bool:
+        neighbors = sum((x + dx, y + dy) in state for dx in (-1, 0, 1) for dy in (-1, 0, 1) if (dx, dy) != (0, 0))
+        if (x, y) in state:
+            return neighbors == 2 or neighbors == 3
+        else:
+            return neighbors == 3
+    next_state: State = set()
+    for x in range(100):
+        for y in range(100):
+            if next_cell_state(x, y):
+                next_state.add((x, y))
+    return next_state
+
+def part1(state: State) -> int:
+    for i in range(100):
+        state = step(state)
+    return len(state)
+
+def part2(state: State) -> int:
+    for i in range(100):
+        state = step(state)
+        state |= {(0, 0), (0, 99), (99, 0), (99, 99)}
+    return len(state)
+
+if __name__ == '__main__':
+    with open('input') as f:
+        state: State = set()
+        for y, line in enumerate(f):
+            for x, c in enumerate(line.strip()):
+                if c == '#':
+                    state.add((x, y))
+    print(part1(state))
+    print(part2(state))