Yea, I just use the types of problems that you’d see on Leetcode or any of the other code practice sites.

The one that I did this morning was:

If given the root of a binary tree, calculate the number of unival subtrees contained in the tree.

The back is usually either blank, or has a space and time complexity that I should get if I did it correctly.

It’s important to make sure you solve it at least once, and understand the solution well before you make a card of it.