helper functions

[jeremymanning]

it'd be nice to have some sample notebooks/code to help with debugging and solving these problems. for example:

• convert a list to a binary tree (and vice versa)
• convert a list to a linked list (and vice versa)
• visualize a binary tree
• define classes for some common data structures (linked list, binary tree)
• implement some classic algorithms-- tree search (BFS, DFS), find common ancestor in a tree, etc.

could add these as we go... 🤔

[jeremymanning]

add a "helpers" folder, with .py files and organized by theme. then populate with relevant data structures and algorithms. and add some .ipynb notebooks (with an Open in Colab badge at the top) to demonstrate the functionality, along with a README.md file in the helpers folder with links to the relevant notebooks/files.