1 files changed, 73 insertions, 0 deletions
diff --git a/2020/12/puzzle-1.c b/2020/12/puzzle-1.c
new file mode 100644
index 0000000..1a4c7ab
--- /dev/null
+++ b/2020/12/puzzle-1.c
@@ -0,0 +1,73 @@
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+main(void)
+{
+	FILE *fp;
+	char cl[5];
+	int north, east;
+	int direction = 0;
+
+	if (!(fp = fopen("input", "r")))
+		err(EXIT_FAILURE, "fopen");
+
+	north = east = 0;
+	while (fgets(cl, sizeof(cl), fp) != NULL) {
+		switch (cl[0]) {
+		case 'N':
+			north += atoi(&cl[1]);
+			break;
+		case 'E':
+			east += atoi(&cl[1]);
+			break;
+		case 'S':
+			north -= atoi(&cl[1]);
+			break;
+		case 'W':
+			east -= atoi(&cl[1]);
+			break;
+		case 'L':
+			direction -= atoi(&cl[1]);
+			goto wrap;
+		case 'R':
+			direction += atoi(&cl[1]);
+
+wrap:
+			/* 0 <= direction < 360 */
+			if (direction >= 360)
+				direction -= 360;
+			else if (direction < 0)
+				direction += 360;
+			break;
+		case 'F':
+			switch (direction) {
+			case 0:
+				east += atoi(&cl[1]);
+				break;
+			case 90:
+				north -= atoi(&cl[1]);
+				break;
+			case 180:
+				east -= atoi(&cl[1]);
+				break;
+			case 270:
+				north += atoi(&cl[1]);
+				break;
+			}
+			break;
+		}
+	}
+	fclose(fp);
+
+	/* Absolute value */
+	if (north < 0)
+		north = -north;
+	if (east < 0)
+		east = -east;
+
+	printf("%d\n", north + east);
+	return EXIT_SUCCESS;
+}