Basic Calculator
Given a string s representing a valid expression Return the result of evaluating the expression Example: s = "1 + 1" => 2 Example: s = " 2-1 + 2 " => 3 Example: s = "(1+(4+5+2)-3)+(6+8)" => 23
Basic Calculator is about exploring choices without getting lost—choose, recurse, undo, repeat. It's a hard one for a reason: it stresses structured exploration when the rules pile up. The gotcha is duplicates and dead ends—good pruning and ordering rules make this manageable.
Meet Coco
Coco is an AI study partner, not a person. She listens while you explain your code, asks what a line does and never hands you the fix. Typing with Coco is free when you sign in, up to a daily limit. Talking with her out loud comes with the $79 pack. Anyone can open the editor and run their code.