1 files changed, 50 insertions, 0 deletions
diff --git a/2018/day12.c b/2018/day12.c
new file mode 100644
index 0000000..5f2f04e
--- /dev/null
+++ b/2018/day12.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef unsigned uint;
+
+enum { Zero = 128, Len = Zero * 2 };
+struct State {
+	char pots[Len];
+};
+
+struct Rule {
+	char pots[5];
+	char next;
+};
+
+int main() {
+	struct State state;
+	memset(state.pots, '.', Len);
+	scanf("initial state: %s\n\n", &state.pots[Zero]);
+	for (uint i = 0; i < Len; ++i) {
+		if (!state.pots[i]) state.pots[i] = '.';
+	}
+
+	uint rulen = 0;
+	struct Rule rules[32];
+	while (!feof(stdin)) {
+		scanf("%5c => %c\n", rules[rulen].pots, &rules[rulen].next);
+		rulen++;
+	}
+
+	for (uint g = 0; g < 20; ++g) {
+		struct State next;
+		memset(next.pots, '.', Len);
+		for (uint i = 2; i < Len - 2; ++i) {
+			for (uint r = 0; r < rulen; ++r) {
+				if (memcmp(&state.pots[i - 2], rules[r].pots, 5)) continue;
+				next.pots[i] = rules[r].next;
+				break;
+			}
+		}
+		state = next;
+	}
+
+	int sum = 0;
+	for (int i = 0; i < Len; ++i) {
+		if (state.pots[i] == '#') sum += i - Zero;
+	}
+	printf("%d\n", sum);
+}