From 6137dd6aa44dcce8f1a8ae0c5959ab7d4a6e24eb Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Wed, 12 Dec 2018 01:48:50 -0500
Subject: Solve day 12 part 2

---
 2018/day12.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/2018/day12.c b/2018/day12.c
index 5f2f04e..d71e592 100644
--- a/2018/day12.c
+++ b/2018/day12.c
@@ -3,8 +3,9 @@
 #include <string.h>
 
 typedef unsigned uint;
+typedef unsigned long ulong;
 
-enum { Zero = 128, Len = Zero * 2 };
+enum { Zero = 256, Len = Zero * 2 };
 struct State {
 	char pots[Len];
 };
@@ -29,7 +30,16 @@ int main() {
 		rulen++;
 	}
 
-	for (uint g = 0; g < 20; ++g) {
+	ulong g;
+	for (g = 0; g < 50000000000L; ++g) {
+		if (g == 20) {
+			int sum = 0;
+			for (int i = 0; i < Len; ++i) {
+				if (state.pots[i] == '#') sum += i - Zero;
+			}
+			printf("%d\n", sum);
+		}
+
 		struct State next;
 		memset(next.pots, '.', Len);
 		for (uint i = 2; i < Len - 2; ++i) {
@@ -39,12 +49,15 @@ int main() {
 				break;
 			}
 		}
+		if (next.pots[2] == '#' || next.pots[Len - 3] == '#') abort();
+
+		if (!memcmp(&next.pots[1], state.pots, Len - 1)) break;
 		state = next;
 	}
 
-	int sum = 0;
-	for (int i = 0; i < Len; ++i) {
-		if (state.pots[i] == '#') sum += i - Zero;
+	long sum = 0;
+	for (long i = 0; i < Len; ++i) {
+		if (state.pots[i] == '#') sum += (50000000000L - g) + i - Zero;
 	}
-	printf("%d\n", sum);
+	printf("%ld\n", sum);
 }
-- 
cgit 1.4.1