Leetcode 22. Generate Parentheses

Generate all distinct well-formed parentheses strings formed from n pairs, i.e., all length-2n sequences where every prefix has at least as many '(' as ')'. This combinatorial generation problem is typically solved with backtracking/DFS by choosing to add '(' or ')' while tracking remaining opens/closes (result count grows as the nth Catalan number; n ≤ 8).