Solution to problem 9 in Python

src/Year_2015/P9.py

@@ -1,3 +1,34 @@
+# --- Day 9: All in a Single Night ---
+
+# Every year, Santa manages to deliver all of his presents in a single night.
+
+# This year, however, he has some new locations to visit; his elves have
+# provided him the distances between every pair of locations. He can start and
+# end at any two (different) locations he wants, but he must visit each
+# location exactly once. What is the shortest distance he can travel to achieve
+# this?
+
+# For example, given the following distances:
+
+# London to Dublin = 464
+# London to Belfast = 518
+# Dublin to Belfast = 141
+
+# The possible routes are therefore:
+
+# Dublin -> London -> Belfast = 982
+# London -> Dublin -> Belfast = 605
+# London -> Belfast -> Dublin = 659
+# Dublin -> Belfast -> London = 659
+# Belfast -> Dublin -> London = 605
+# Belfast -> London -> Dublin = 982
+
+# The shortest of these is London -> Dublin -> Belfast = 605, and so the answer
+# is 605 in this example.
+
+# What is the distance of the shortest route?
+
+
 from itertools import permutations
 
 import networkx as nx
@@ -21,5 +52,29 @@ for f, t in permutations(cycle, 2):
         if len(path) == len(cycle) - 1:
             paths.append(path_weight(G, path, weight="weight"))
 
-print(f"Solution part 1: {min(paths)}")
-print(f"Solution part 2: {max(paths)}")
+
+def part_1() -> None:
+    print(f"Solution part 1: {min(paths)}")
+
+
+# --- Part Two ---
+
+# The next year, just to show off, Santa decides to take the route with the
+# longest distance instead.
+
+# He can still start and end at any two (different) locations he wants, and he
+# still must visit each location exactly once.
+
+# For example, given the distances above, the longest route would be 982 via
+# (for example) Dublin -> London -> Belfast.
+
+# What is the distance of the longest route?
+
+
+def part_2() -> None:
+    print(f"Solution part 2: {max(paths)}")
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()