Count pairs from two BSTs whose sum is equal to given value x

Count pairs from two BSTs whose sum is equal to given value x is a DSA topic. In plain words you use it for folder on disk in a file explorer. Don’t start with a slogan — start with that picture.

Smallest example: left < root < right. Type it, run it, and say what you see. If you can do that from memory, you know Count pairs from two BSTs whose sum is equal to given value x.

From the example next to this theory — Count pairs from two BSTs whose sum is equal to given value x: dry-run [4, 1, 3].

Trap — unbalanced BST becoming a list. Fix that before you talk about advanced DSA.

Viva: what is Count pairs from two BSTs whose sum is equal to given value x? Then show left < root < right. Then name the trap.