Valid Parentheses Matching — Stack Patterns

The Valid Parentheses Matching pattern applies when you need the Valid Parentheses Matching technique within the Stack Patterns pattern. Its time complexity is O(n) and space complexity O(n). It is used in 6 problems on Thita, including Longest Valid Parentheses, Minimum Add to Make Parentheses Valid and Minimum Number of Swaps to Make the String Balanced. Common variations are Largest Rectangle in Histogram and Monotonic Stack.

Master parentheses validation and balancing using stack. Handle multiple bracket types and minimum additions.

Valid Parentheses Matching is one of the 6 subpatterns of the Stack Patterns pattern, which covers parentheses matching, monotonic stack, histogram, and expression evaluation. The whole pattern is about 2.5 hours of study. This subpattern is a core technique: expect it to come up directly in interviews.

What Valid Parentheses Matching covers

Master stack-based algorithms including valid parentheses, monotonic stack for next greater element, expression evaluation, and histogram problems. Problems in this subpattern are usually searched for as valid parentheses, bracket matching, balanced parentheses, stack parentheses, leetcode 20.

How to practise Valid Parentheses Matching on Thita.ai

Read the theory for Valid Parentheses Matching, then work the problems attached to it in the browser editor. Your solution runs against the problem's test cases, and the AI coach offers a hint about the technique you are missing rather than a finished solution. Progress is tracked per subpattern, so the Stack Patterns tracker shows this one as covered once you have solved its problems.

Other subpatterns in Stack Patterns

• Monotonic Stack — Master monotonic stack for next greater element, daily temperatures, and stock span problems.
• Largest Rectangle in Histogram — Learn the stack-based approach to find largest rectangle in histogram and maximal rectangle in matrix.
• Stack - Min Stack Design — Design a stack that supports push, pop, top, and retrieving minimum element in constant time.
• Simulation / Backtracking Helper — Use stack for simulation problems like simplify path, decode string, and asteroid collision.
• Expression Evaluation (RPN/Infix) — Master expression evaluation using stack. Evaluate reverse polish notation and basic calculator problems.

Related DSA patterns

• Array/Matrix Manipulation Patterns — In-place operations, hashing, prefix sums, spiral traversal, and cyclic sort.
• Linked List Manipulation Patterns — In-place reversal, merging sorted lists, reordering, and intersection detection.
• String Manipulation Patterns — Palindrome checking, anagram detection, pattern matching, and string conversion.
• Tree Traversal Patterns (DFS & BFS) — Preorder, inorder, level order traversal, LCA, and serialization.

Where to go next

Valid Parentheses Matching is one lesson in a 16-pattern DSA course. If you are preparing end to end, work the interview-critical patterns first and use the pattern sheet as the checklist; if you are here for one technique, the Stack Patterns guide is the shortest path back to the rest of it.

• The Stack Patterns pattern guide
• All DSA patterns
• The DSA patterns sheet
• Coding practice