Added first solution of day 11

1 files changed, 94 insertions, 0 deletions

diff --git a/2020/11/solve.c b/2020/11/solve.c
new file mode 100644
index 0000000..6fd8691
--- /dev/null
+++ b/2020/11/solve.c
@@ -0,0 +1,94 @@
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define SIZE 10000
+#define X_MAX 99
+#define Y_MAX 97
+
+// Quite magical, isn't it?
+#define ADJACENT(x, y, p)                                                                          \
+	(x != 0 && y != 0 ? *(p - X_MAX - 1) == '#' : 0) + (y != 0 ? *(p - X_MAX) == '#' : 0) +    \
+		(x != X_MAX && y != 0 ? *(p - X_MAX + 1) == '#' : 0) +                             \
+		(x != 0 ? *(p - 1) == '#' : 0) + (x != X_MAX ? *(p + 1) == '#' : 0) +              \
+		(x != 0 && y != Y_MAX ? *(p + X_MAX - 1) == '#' : 0) +                             \
+		(y != Y_MAX ? *(p + X_MAX) == '#' : 0) +                                           \
+		(x != X_MAX && y != Y_MAX ? *(p + X_MAX + 1) == '#' : 0);
+
+int count(char *buf1, char *buf2)
+{
+	int x = 0, y = 0;
+	for (char *p = buf1; *p; p++) {
+		if (*p == '.') {
+			x++;
+			buf2[p - buf1] = '.';
+			continue;
+		}
+
+		if (*p == '\n') {
+			x = 0;
+			y++;
+			buf2[p - buf1] = '\n';
+			continue;
+		}
+
+		int cnt = ADJACENT(x, y, p);
+
+		if (*p == 'L' && !cnt) {
+			buf2[p - buf1] = '#';
+		} else if (*p == '#' && cnt >= 4) {
+			buf2[p - buf1] = 'L';
+		} else {
+			buf2[p - buf1] = *p;
+		}
+
+		x++;
+	}
+
+	if (memcmp(buf1, buf2, SIZE)) {
+		return count(buf2, buf1); // Swap buffers
+	} else {
+		int cnt = 0;
+		for (char *p = buf1; *p; p++) {
+			if (*p == '#')
+				cnt++;
+		}
+		return cnt;
+	}
+}
+
+int part_one(char *data)
+{
+	int res = 0;
+
+	char buf1[SIZE] = { 0 };
+	memcpy(buf1, data, SIZE);
+	char buf2[SIZE] = { 0 };
+	memcpy(buf2, data, SIZE);
+
+	return count(buf1, buf2);
+}
+
+int part_two(char *data)
+{
+	int res = 0;
+
+	return res;
+}
+
+int main(int argc, char *argv[])
+{
+	FILE *fp = fopen("input", "r");
+	if (!fp)
+		exit(EXIT_FAILURE);
+	char buf[SIZE] = { 0 };
+	fread(buf, SIZE, 1, fp);
+
+	printf("%d\n", part_one(buf));
+	printf("%d\n", part_two(buf));
+
+	fclose(fp);
+	return 0;
+}