Workout #30: Flatten a List

Write a function that takes a list of lists (just one element deep) and returns a flat, one-dimensional version of the list. Thus, invoking

flatten([[1,2], [3,4]])

will return

[1,2,3,4]

TRY IT YOURSELF

ANSWER

https://colab.research.google.com/drive/1hqxjLja8m0roUG4I9HQmoMZShd31UDZ1?usp=sharing