Solution to problem 12 part 2 in Python

src/P12.py

@@ -1,3 +1,5 @@
+import math
+
 # --- Day 12: Rain Risk ---
 
 # Your ferry made decent progress toward the island, but the storm came in
@@ -87,5 +89,97 @@ def part_1() -> None:
     print(f"The Manhattan distance is {manhattan_distance}")
 
 
+# --- Part Two ---
+
+# Before you can give the destination to the captain, you realize that the
+# actual action meanings were printed on the back of the instructions the whole
+# time.
+
+# Almost all of the actions indicate how to move a waypoint which is relative
+# to the ship's position:
+
+#     Action N means to move the waypoint north by the given value.
+#     Action S means to move the waypoint south by the given value.
+#     Action E means to move the waypoint east by the given value.
+#     Action W means to move the waypoint west by the given value.
+#     Action L means to rotate the waypoint around the ship left
+# (counter-clockwise) the given number of degrees.
+#     Action R means to rotate the waypoint around the ship right (clockwise)
+# the given number of degrees.
+#     Action F means to move forward to the waypoint a number of times equal to
+# the given value.
+
+# The waypoint starts 10 units east and 1 unit north relative to the ship. The
+# waypoint is relative to the ship; that is, if the ship moves, the waypoint
+# moves with it.
+
+# For example, using the same instructions as above:
+
+#     F10 moves the ship to the waypoint 10 times (a total of 100 units east
+# and 10 units north), leaving the ship at east 100, north 10. The waypoint
+# stays 10 units east and 1 unit north of the ship.
+#     N3 moves the waypoint 3 units north to 10 units east and 4 units north of
+# the ship. The ship remains at east 100, north 10.
+#     F7 moves the ship to the waypoint 7 times (a total of 70 units east and
+# 28 units north), leaving the ship at east 170, north 38. The waypoint stays
+# 10 units east and 4 units north of the ship.
+#     R90 rotates the waypoint around the ship clockwise 90 degrees, moving it
+# to 4 units east and 10 units south of the ship. The ship remains at east 170,
+# north 38.
+#     F11 moves the ship to the waypoint 11 times (a total of 44 units east and
+# 110 units south), leaving the ship at east 214, south 72. The waypoint stays
+# 4 units east and 10 units south of the ship.
+
+# After these operations, the ship's Manhattan distance from its starting
+# position is 214 + 72 = 286.
+
+# Figure out where the navigation instructions actually lead. What is the
+# Manhattan distance between that location and the ship's starting position?
+
+
+def part_2() -> None:
+
+    ship_pos = [0, 0]
+    waypoint_pos = [10, 1]
+    waypoint_dir = 0
+
+    for instr in instructions:
+        _dir, _num = instr[:1], instr[1:]
+        if _dir == "E":
+            waypoint_pos[0] += int(_num)
+        elif _dir == "W":
+            waypoint_pos[0] -= int(_num)
+        elif _dir == "N":
+            waypoint_pos[1] += int(_num)
+        elif _dir == "S":
+            waypoint_pos[1] -= int(_num)
+        elif _dir == "F":
+            ship_pos[0] += int(_num) * waypoint_pos[0]
+            ship_pos[1] += int(_num) * waypoint_pos[1]
+        else:
+            if _dir == "R":
+                # rotations are clockwise
+                _num = str(360 - int(_num))
+            waypoint_dir += int(_num)
+            # avoid rotation overflow
+            waypoint_dir %= 360
+            # convert to radians to make life easier
+            radians = math.radians(int(_num))
+            waypoint_pos = [
+                round(
+                    (waypoint_pos[0] * math.cos(radians))
+                    - (waypoint_pos[1] * math.sin(radians))
+                ),
+                round(
+                    (waypoint_pos[0] * math.sin(radians))
+                    + (waypoint_pos[1] * math.cos(radians))
+                ),
+            ]
+
+    manhattan_distance = abs(ship_pos[0]) + abs(ship_pos[1])
+    print(f"The Manhattan distance is {manhattan_distance}")
+
+
 if __name__ == "__main__":
     part_1()
+    part_2()