1 files changed, 57 insertions, 0 deletions
diff --git a/2020/03/solve.c b/2020/03/solve.c
new file mode 100644
index 0000000..2f6312b
--- /dev/null
+++ b/2020/03/solve.c
@@ -0,0 +1,57 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int part_one(FILE *fp)
+{
+	int res = 0;
+
+	char *line = NULL;
+	size_t len = 0, strlen = 0;
+	int curr = 0;
+	while ((strlen = getline(&line, &len, fp)) != -1) {
+		if (line[curr % (strlen - 1)] == '#')
+			res++;
+		curr += 3;
+	}
+
+	return res;
+}
+
+#define DOWN_TWO (1 << 15)
+int part_two(FILE *fp)
+{
+	int final = 1;
+	int opt[] = { 1, 3, 5, 7, 1 | DOWN_TWO };
+
+	char *line = NULL;
+	size_t len = 0, strlen = 0;
+	for (int i = 0; i < sizeof(opt) / sizeof(opt[0]); i++) {
+		int res = 0, row = 0, curr = 0;
+		while ((strlen = getline(&line, &len, fp)) != -1) {
+			if (row++ % 2 == 1 && opt[i] & DOWN_TWO)
+				continue;
+			if (line[curr % (strlen - 1)] == '#')
+				res++;
+			curr += opt[i] & ~DOWN_TWO;
+		}
+		rewind(fp);
+		final *= res;
+	}
+
+	return final;
+}
+
+int main(int argc, char *argv[])
+{
+	FILE *fp = fopen("input", "r");
+	if (!fp)
+		exit(EXIT_FAILURE);
+
+	printf("%d\n", part_one(fp));
+	rewind(fp);
+	printf("%u\n", part_two(fp));
+
+	fclose(fp);
+	return 0;
+}