Solution to problem 3 in Python

src/Year_2015/P3.py

@@ -58,5 +58,58 @@ def part_1() -> None:
     print(f"{len(set(pos))} houses receive at least one present")
 
 
+# --- Part Two ---
+
+# The next year, to speed up the process, Santa creates a robot version of
+# himself, Robo-Santa, to deliver presents with him.
+
+# Santa and Robo-Santa start at the same location (delivering two presents to
+# the same starting house), then take turns moving based on instructions from
+# the elf, who is eggnoggedly reading from the same script as the previous
+# year.
+
+# This year, how many houses receive at least one present?
+
+# For example:
+
+#     ^v delivers presents to 3 houses, because Santa goes north, and then
+# Robo-Santa goes south.
+#     ^>v< now delivers presents to 3 houses, and Santa and Robo-Santa end up
+# back where they started.
+#     ^v^v^v^v^v now delivers presents to 11 houses, with Santa going one
+# direction and Robo-Santa going the other.
+
+
+def part_2():
+    santa = [(0, 0)]
+    robo_santa = [(0, 0)]
+    for idx, move in enumerate(moves):
+        if move == "^":
+            if idx % 2 == 0:
+                santa.append(move_up(santa[-1]))
+            else:
+                robo_santa.append(move_up(robo_santa[-1]))
+        elif move == "v":
+            if idx % 2 == 0:
+                santa.append(move_down(santa[-1]))
+            else:
+                robo_santa.append(move_down(robo_santa[-1]))
+        elif move == "<":
+            if idx % 2 == 0:
+                santa.append(move_left(santa[-1]))
+            else:
+                robo_santa.append(move_left(robo_santa[-1]))
+        elif move == ">":
+            if idx % 2 == 0:
+                santa.append(move_right(santa[-1]))
+            else:
+                robo_santa.append(move_right(robo_santa[-1]))
+
+    print(
+        f"{len(set(santa + robo_santa))} houses receive at least one present"
+    )
+
+
 if __name__ == "__main__":
     part_1()
+    part_2()