Count All Valid Pickup and Delivery Options - LeetCode 1359 - Python - Memoization - Combinatorics

Solution, explanation, and complexity analysis for LeetCode 1359, the problem of the day for September 10th, in Python. I go over the memoization solution and the math solution. Problem Description: https://leetcode.com/problems/count-all-valid-pickup-and-delivery-options Code: https://drive.google.com/file/d/1Ww6I6h8YCYqMyyJ4w46amfxnlGq8NEbc/view?usp=sharing