Part 1 was easily solved by Dijkstras (using heapq).
Tricky part was to find the way to serialize the
queue items for the heappush and heappop to behave
as required.
Part 2 was incredible hard to figure out, and I
could not do it by myself. From the subreddit, it
is hinted that a traditional set of visited nodes
to determine algorithm exit would not work.
After some laboration and readin some hints, I
managed to find a solution where the code keeps
tracks using a defaultdict.
Anders Englöf Ytterström
7c2b4c835a