1 files changed, 158 insertions, 0 deletions
diff --git a/2020/11/puzzles.c b/2020/11/puzzles.c
new file mode 100644
index 0000000..7c579b9
--- /dev/null
+++ b/2020/11/puzzles.c
@@ -0,0 +1,158 @@
+#include <err.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#define ROWCNT 98
+#define ROWLEN 98
+
+#ifdef PART2
+	#define IS_SEAT(a, b)                                                                              \
+		if (rows[a][b] == '.')                                                             \
+		continue
+	#define IS_OCC(a, b)                                                                               \
+		if (rows[a][b] == '#')                                                             \
+		adjecent++
+#endif
+
+bool changed;
+char rows[ROWCNT][ROWLEN + 1];
+char temp[ROWCNT][ROWLEN + 1];
+
+/* Check and update a seat at the given index */
+static void
+check_seat(int const i, int const j)
+{
+	if (rows[i][j] == '.')
+		return;
+
+	int adjecent = 0;
+
+#ifdef PART2
+	/* Up */
+	for (int h = i - 1; h >= 0; h--) {
+		IS_SEAT(h, j);
+		IS_OCC(h, j);
+		break;
+	}
+	/* Down */
+	for (int h = i + 1; h < ROWCNT; h++) {
+		IS_SEAT(h, j);
+		IS_OCC(h, j);
+		break;
+	}
+	/* Left */
+	for (int h = j - 1; h >= 0; h--) {
+		IS_SEAT(i, h);
+		IS_OCC(i, h);
+		break;
+	}
+	/* Right */
+	for (int h = j + 1; h < ROWLEN; h++) {
+		IS_SEAT(i, h);
+		IS_OCC(i, h);
+		break;
+	}
+	/* Up-Left */
+	for (int h = i - 1, k = j - 1; h >= 0 && k >= 0; h--, k--) {
+		IS_SEAT(h, k);
+		IS_OCC(h, k);
+		break;
+	}
+	/* Up-Right */
+	for (int h = i - 1, k = j + 1; h >= 0 && k < ROWLEN; h--, k++) {
+		IS_SEAT(h, k);
+		IS_OCC(h, k);
+		break;
+	}
+	/* Down-Left */
+	for (int h = i + 1, k = j - 1; h < ROWCNT && k >= 0; h++, k--) {
+		IS_SEAT(h, k);
+		IS_OCC(h, k);
+		break;
+	}
+	/* Down-Right */
+	for (int h = i + 1, k = j + 1; h < ROWCNT && k < ROWLEN; h++, k++) {
+		IS_SEAT(h, k);
+		IS_OCC(h, k);
+		break;
+	}
+#else
+	for (int h = i - 1; h <= i + 1; h++) {
+		if (h < 0 || h > ROWCNT - 1)
+			continue;
+		for (int k = j - 1; k <= j + 1; k++) {
+			if (k < 0 || k > ROWCNT - 1 || (h == i && k == j))
+				continue;
+			if (rows[h][k] == '#')
+				adjecent++;
+		}
+	}
+#endif
+	/* Edit seats as needed */
+	if (rows[i][j] == 'L' && adjecent == 0) {
+		temp[i][j] = '#';
+		changed = true;
+#ifdef PART2
+	} else if (rows[i][j] == '#' && adjecent >= 5) {
+#else
+	} else if (rows[i][j] == '#' && adjecent >= 4) {
+#endif
+		temp[i][j] = 'L';
+		changed = true;
+	} else
+		temp[i][j] = rows[i][j];
+}
+
+int
+main(void)
+{
+	/* Initialize the temp array to be all floor */
+	int i, j;
+	for (i = 0; i < ROWCNT; i++) {
+		for (j = 0; j < ROWLEN; j++)
+			temp[i][j] = '.';
+	}
+
+	FILE *fp;
+	if (!(fp = fopen("input", "r")))
+		err(EXIT_FAILURE, "fopen");
+
+	/* Read in seats */
+	i = j = 0;
+	char c;
+	while ((c = fgetc(fp)) != EOF) {
+		if (c == '\n') {
+			i = 0;
+			j++;
+		} else
+			rows[j][i++] = c;
+	}
+	fclose(fp);
+
+	/* Update the seats until they don't change anymore */
+	do {
+		changed = false;
+		for (i = 0; i < ROWCNT; i++) {
+			for (j = 0; j < ROWLEN; j++)
+				check_seat(i, j);
+		}
+
+		for (i = 0; i < ROWCNT; i++) {
+			for (j = 0; j < ROWLEN; j++)
+				rows[i][j] = temp[i][j];
+		}
+	} while (changed);
+
+	/* Calculate filled seats */
+	int count = 0;
+	for (i = 0; i < ROWCNT; i++) {
+		for (j = 0; j < ROWLEN; j++) {
+			if (rows[i][j] == '#')
+				count++;
+		}
+	}
+
+	printf("%d\n", count);
+	return EXIT_SUCCESS;
+}