From e06b2d1c4fcbafecc66b0992f0264153f1f062d6 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Thu, 17 Dec 2020 14:04:56 -0500
Subject: Solve day 17 part 2

---
 2020/day17.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 55 insertions(+), 11 deletions(-)

(limited to '2020/day17.c')

diff --git a/2020/day17.c b/2020/day17.c
index 6cab278..620563f 100644
--- a/2020/day17.c
+++ b/2020/day17.c
@@ -1,10 +1,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-struct Dim {
+struct Dim3 {
 	char _[32][32][32];
 };
-static int neighbors(const struct Dim *d, int z, int y, int x) {
+static int neighbors3(const struct Dim3 *d, int z, int y, int x) {
 	int active = 0;
 	for (int i = -1; i <= +1; ++i)
 	for (int j = -1; j <= +1; ++j)
@@ -14,12 +14,12 @@ static int neighbors(const struct Dim *d, int z, int y, int x) {
 	}
 	return active;
 }
-static struct Dim step(const struct Dim *prev) {
-	struct Dim next;
+static struct Dim3 step3(const struct Dim3 *prev) {
+	struct Dim3 next;
 	for (int z = 0; z < 32; ++z)
 	for (int y = 0; y < 32; ++y)
 	for (int x = 0; x < 32; ++x) {
-		int active = neighbors(prev, z, y, x);
+		int active = neighbors3(prev, z, y, x);
 		if (prev->_[z][y][x] == '#') {
 			next._[z][y][x] = (active == 2 || active == 3 ? '#' : '.');
 		} else {
@@ -28,21 +28,65 @@ static struct Dim step(const struct Dim *prev) {
 	}
 	return next;
 }
+struct Dim4 {
+	char _[32][32][32][32];
+};
+static int neighbors4(const struct Dim4 *d, int w, int z, int y, int x) {
+	int active = 0;
+	for (int i = -1; i <= +1; ++i)
+	for (int j = -1; j <= +1; ++j)
+	for (int k = -1; k <= +1; ++k)
+	for (int l = -1; l <= +1; ++l) {
+		if (!i && !j && !k && !l) continue;
+		active += (d->_[w+i&31][z+j&31][y+k&31][x+l&31] == '#');
+	}
+	return active;
+}
+static struct Dim4 step4(const struct Dim4 *prev) {
+	struct Dim4 next;
+	for (int w = 0; w < 32; ++w)
+	for (int z = 0; z < 32; ++z)
+	for (int y = 0; y < 32; ++y)
+	for (int x = 0; x < 32; ++x) {
+		int active = neighbors4(prev, w, z, y, x);
+		if (prev->_[w][z][y][x] == '#') {
+			next._[w][z][y][x] = (active == 2 || active == 3 ? '#' : '.');
+		} else {
+			next._[w][z][y][x] = (active == 3 ? '#' : '.');
+		}
+	}
+	return next;
+}
 int main(void) {
-	struct Dim init = {0};
+	struct Dim3 init3 = {0};
+	struct Dim4 init4 = {0};
 	for (int y = 0;; ++y) {
-		if (scanf("%s\n", init._[0][y]) < 1) break;
+		if (scanf("%s\n", init3._[0][y]) < 1) break;
+		strcpy(init4._[0][0][y], init3._[0][y]);
 	}
-	struct Dim prev = init;
+	struct Dim3 prev3 = init3;
 	for (int i = 0; i < 6; ++i) {
-		struct Dim next = step(&prev);
-		prev = next;
+		struct Dim3 next3 = step3(&prev3);
+		prev3 = next3;
 	}
 	int active = 0;
 	for (int z = 0; z < 32; ++z)
 	for (int y = 0; y < 32; ++y)
 	for (int x = 0; x < 32; ++x) {
-		active += (prev._[z][y][x] == '#');
+		active += (prev3._[z][y][x] == '#');
+	}
+	printf("%d\n", active);
+	struct Dim4 prev4 = init4;
+	for (int i = 0; i < 6; ++i) {
+		struct Dim4 next4 = step4(&prev4);
+		prev4 = next4;
+	}
+	active = 0;
+	for (int w = 0; w < 32; ++w)
+	for (int z = 0; z < 32; ++z)
+	for (int y = 0; y < 32; ++y)
+	for (int x = 0; x < 32; ++x) {
+		active += (prev4._[w][z][y][x] == '#');
 	}
 	printf("%d\n", active);
 }
-- 
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