Questions corresponding to the script can be found here: Advent of Code 2019

Recursion does the trick.

• intList = list(map(int, stringList)) to convert a list of string to list of int.
• recursion does the trick again.
• Another thing to note is using copy.deepcopy() to create a copy of a list (reference type)
  • 2019/12/03 UPDATE: duplicating list can also be done by l2 = l1[:]

There might be a better data structure for the paths - I chose to record every point that it crossed. The data size is not that big so performance was ok. I did encounter performance issue trying to find the common coordinates of the two paths. At first, I was using:

listOfCross = []
for point in firstCoordinates:
    if point in secondCoordinates:
        listOfCross.append(point)

It was slow. A bit of research and I found this thread on StackOverflow

listOfCross = list(set(firstCoordinates).intersection(secondCoordinates))

Neat.

Jonathan Paulson’s solution is really elegant.

This one was pretty straight-forward. Most of time was spent on understand the requirement of part 2.

Could have read in the number as string to get the digits.