How do you check for balanced parentheses using a Stack?

Balanced Parentheses

javascript

1
Time complexity: O(n).
2
Auxiliary space: O(n) in the worst case.
3
The Stack captures nested structure naturally.
4
A closing delimiter without an opening delimiter is invalid.
5
Any unmatched opening delimiter remaining at the end makes the expression invalid.

Difficulty: 3/10

Topics: Stacks, String Parsing, Algorithm Design

0-2 years experience

1
We are building a simple markdown editor and want to highlight unmatched brackets like parentheses, square brackets, and curly braces as the user types. How would you write a helper function to validate if the current line has balanced brackets?
2
Imagine you wrote a bracket validator using a stack, but it's returning true for the input '(]'. Walk me through how you would debug this and what the stack state looks like at each step.

2-5 years experience

1
We're adding a feature to a code editor that auto-closes brackets. Sometimes users paste code snippets with mixed, nested brackets and quotes, like const x = "{[(]". How would you extend a basic stack-based validator to ignore brackets inside string literals or comments?
2
A teammate implemented a bracket matcher for a configuration file parser using a stack, but it's throwing an EmptyStackException on certain malformed inputs. Where in the logic is this likely happening, and how would you refactor it to fail gracefully with a helpful error message?

5-8 years experience

1
We need to validate syntax for massive SQL scripts up to 2GB uploaded by users. A naive in-memory stack-based validation will cause Out-Of-Memory errors. How would you design a memory-efficient validation service that can handle these large files streamingly?
2
You are designing the syntax-checking engine for an IDE extension. It needs to run on every keystroke. How would you optimize a stack-based validator to avoid re-parsing the entire file from scratch every time a user types a single character?

8+ years experience

1
Our platform supports multiple domain-specific languages, each with different bracket rules, string escape behaviors, and comment styles. How would you architect a highly extensible, reusable parsing framework that teams can easily configure for their specific DSL without rewriting the core validation engine?
2
We are migrating our legacy monolithic parser to a distributed, event-driven architecture where configuration payloads are validated at the API gateway. How do you balance the latency overhead of running deep syntax validation like bracket matching at the gateway versus deferring it to downstream microservices?

❓How would you optimize this if we only had one type of parentheses, say just round brackets?
❓What if the input string is too large to fit in memory, like a 10GB JSON file?
❓How do you handle escape characters or brackets inside string literals?