Minimum Add to Make Parentheses Valid Coding Problem

“Minimum Add to Make Parentheses Valid” is one of those deceptively simple string problems that shows up a lot in coding interviews because it tests whether you truly understand balanced parentheses, not whether you can write fancy code. You’re given a string made up of just ( and ) . Your goal is to figure out the minimum number of parentheses you must add (anywhere in the string) to make the entire string valid. A valid parentheses string follows two rules: Every opening parenthesis ( must be matched with a closing parenthesis ) . At no point while scanning left to right should you have more ) than ( . (Because a closing parenthesis can’t match something that hasn’t appeared yet.) So strings like () and (())() are valid. Strings like (() or ())( are not. What makes this problem useful for interview prep is that you’re not asked to “fix” the string explicitly; you’re asked to count the minimum insertions needed to make it valid. Want to explore more coding problem solutions? Check out