1 files changed, 115 insertions, 0 deletions
diff --git a/2021/03/solve.c b/2021/03/solve.c
new file mode 100644
index 0000000..87317c8
--- /dev/null
+++ b/2021/03/solve.c
@@ -0,0 +1,115 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define FORLINE                                                                                    \
+	char *line = NULL;                                                                         \
+	size_t size = 0;                                                                           \
+	while (getline(&line, &size, fp) != EOF)
+#define FREELINE                                                                                   \
+	if (line)                                                                                  \
+	free(line)
+
+#define FORCH                                                                                      \
+	char ch = 0;                                                                               \
+	while ((ch = fgetc(fp)) != EOF)
+
+#define WHOLE                                                                                      \
+	fseek(fp, 0, SEEK_END);                                                                    \
+	long fsize = ftell(fp);                                                                    \
+	fseek(fp, 0, SEEK_SET);                                                                    \
+	char *data = malloc(fsize + 1);                                                            \
+	fread(data, 1, fsize, fp);                                                                 \
+	data[fsize] = 0;                                                                           \
+	data[fsize--] = 0
+
+/* #define LINES 1000 */
+/* #define HALF (LINES / 2) // Half of line count */
+/* #define WIDTH 12 // Binary width */
+#define LINES 12
+#define HALF (LINES / 2)
+#define WIDTH 5
+
+static int part_one(FILE *fp)
+{
+	int bits[WIDTH] = { 0 };
+	FORLINE
+	for (int i = 0; i < WIDTH; i++)
+		bits[i] += line[i] == '0' ? 0 : 1;
+	FREELINE;
+
+	int epsilon = 0, gamma = 0;
+	for (int i = 0; i < WIDTH; i++)
+		if (bits[i] > HALF)
+			gamma |= (1 << (WIDTH - i - 1));
+		else
+			epsilon |= (1 << (WIDTH - i - 1));
+
+	return epsilon * gamma;
+}
+
+#define ISSET(num, n) (((num) & (1 << (n))) >> (n))
+#define TENDENCY(num, n) (ISSET(num, n) ? 1 : -1)
+static int part_two(FILE *fp)
+{
+	int res = 0;
+
+	int binaries[LINES] = { 0 };
+	int i = 0;
+	FORLINE
+	binaries[i++] = strtol(line, NULL, 2);
+	FREELINE;
+
+	int generator = (1 << WIDTH) - 1, scrubber = (1 << WIDTH) - 1; // masks
+	/* printf("msk %d\n", generator); */
+	for (int x = WIDTH; x > 0; x--) {
+		printf("\n%d. bit\n", x - 1);
+		int generator_tendency = 0, scrubber_tendency = 0;
+		for (int y = 0; y < LINES; y++) {
+			if ((binaries[y] >> x) == (generator >> x)) {
+				/* printf("%d: %d %d\n", binaries[y], binaries[y] >> x, */
+				/*        generator >> x); */
+				generator_tendency += TENDENCY(binaries[y], x - 1);
+			}
+
+			if ((binaries[y] >> x) == (scrubber >> x)) {
+				/* printf("%d: %d %d\n", binaries[y], binaries[y] >> x, scrubber >> x); */
+				scrubber_tendency += TENDENCY(binaries[y], x - 1);
+			}
+		}
+		if (generator_tendency < 0)
+			generator &= ~(1 << (x - 1)); // Clear bit
+		if (scrubber_tendency >= 0)
+			scrubber &= ~(1 << (x - 1)); // Clear bit
+		/* printf("tnd %d\n", generator_tendency); */
+		/* printf("msk %d\n", generator); */
+		printf("tnd %d\n", scrubber_tendency);
+		printf("msk %d\n", scrubber);
+	}
+
+	printf("res %d %d\n", generator, scrubber);
+
+	// generator = 1459
+	// scrubber = 3178
+	return generator * scrubber;
+}
+
+int main(int argc, char *argv[])
+{
+	(void)argc;
+	(void)argv;
+
+	FILE *fp = fopen("input", "r");
+	if (!fp)
+		exit(EXIT_FAILURE);
+
+	clock_t tic = clock();
+	printf("%d\n", part_one(fp));
+	rewind(fp);
+	printf("%d\n", part_two(fp));
+	clock_t toc = clock();
+	printf("TIME: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
+
+	fclose(fp);
+	return 0;
+}