1 files changed, 102 insertions, 0 deletions
diff --git a/day12/day12.py b/day12/day12.py
new file mode 100644
index 0000000..2476725
--- /dev/null
+++ b/day12/day12.py
@@ -0,0 +1,102 @@
+"""Day 12."""
+import math
+
+with open("input") as f:
+    instructions = f.read().rstrip().split("\n")
+
+DIRECTIONS = ("N", "E", "S", "W")
+CURRENT_DIRECTION = "E"
+CORDS = {
+    "x": 0,
+    "y": 0,
+}
+WAYPOINT = {
+    'x': 10,
+    'y': 1,
+}
+
+
+def left(current_direction, degree):
+    idx = DIRECTIONS.index(current_direction) - (degree // 90)
+    return DIRECTIONS[idx % len(DIRECTIONS)]
+
+
+def right(current_direction, degree):
+    idx = DIRECTIONS.index(current_direction) + (degree // 90)
+    return DIRECTIONS[idx % len(DIRECTIONS)]
+
+
+def update_coords(direction, value):
+    if direction == "N":
+        CORDS["y"] += value
+    if direction == "E":
+        CORDS["x"] += value
+    if direction == "S":
+        CORDS["y"] -= value
+    if direction == "W":
+        CORDS["x"] -= value
+
+
+for inst in instructions:
+    direction, value = inst[0], int(inst[1:])
+    if direction == "L":
+        CURRENT_DIRECTION = left(CURRENT_DIRECTION, value)
+    elif direction == "R":
+        CURRENT_DIRECTION = right(CURRENT_DIRECTION, value)
+    elif direction == "F":
+        update_coords(CURRENT_DIRECTION, value)
+    else:
+        update_coords(direction, value)
+
+# Part 1
+part_1 = abs(CORDS["x"]) + abs(CORDS["y"])
+print(part_1)
+assert part_1 == 882
+
+# reset coords
+CORDS = {
+    "x": 0,
+    "y": 0,
+}
+
+def update_waypoint(direction, value):
+    if direction == "N":
+        WAYPOINT["y"] += value
+    if direction == "E":
+        WAYPOINT["x"] += value
+    if direction == "S":
+        WAYPOINT["y"] -= value
+    if direction == "W":
+        WAYPOINT["x"] -= value
+
+
+def clockwise(degrees):
+    """rotate clockwise."""
+    x = WAYPOINT["x"]
+    y = WAYPOINT["y"]
+    rads = math.radians(degrees % 360)
+    return (
+        round(x * math.cos(rads) + y * math.sin(rads)),
+        round(-x * math.sin(rads) + y * math.cos(rads))
+    )
+
+for inst in instructions:
+    direction, value = inst[0], int(inst[1:])
+    if direction == "L":
+        newx, newy = clockwise(360 - value)
+        WAYPOINT["x"] = newx
+        WAYPOINT["y"] = newy
+    elif direction == "R":
+        newx, newy = clockwise(value)
+        WAYPOINT["x"] = newx
+        WAYPOINT["y"] = newy
+    elif direction == "F":
+        CORDS["x"] += WAYPOINT["x"] * value
+        CORDS["y"] += WAYPOINT["y"] * value
+    else:
+        update_waypoint(direction, value)
+
+
+part_2 = abs(CORDS["x"]) + abs(CORDS["y"])
+assert part_2 == 28885
+print(part_2)