Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Meta SWE coding round with a bracket matching problem. Pretty standard stuff but worth knowing cold if you're prepping for this loop.

Questions Asked (1)

Given a string that may contain brackets of three types, [], {}, and (), write a function to determine whether the bracket usage in the string is valid. An empty string counts as valid, and brackets must be closed in the correct order and matching type.

Algorithms & Data Structures

Author's notes

Stack-based solution, pretty much what you'd expect.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Use a stack to track opening brackets. Iterate through the string, pushing opening brackets and popping when a closing bracket matches the top of the stack. At the end, the stack should be empty for a valid string.

Pro tip: Clarify edge cases upfront (empty string, non-bracket characters) and discuss time/space complexity (O(n) time, O(n) space) to demonstrate thoroughness.

1. Clarify requirements and edge cases

Ask if the string can contain non-bracket characters and confirm that empty string is valid. Discuss examples like '()[]{}' (valid) and '([)]' (invalid).

2. Choose data structure and algorithm

Explain that a stack is ideal because brackets follow LIFO order. Outline the algorithm: iterate through each character, push opening brackets, and for closing brackets, check if the stack top matches.

3. Walk through the algorithm with an example

Trace through a sample string like '{[()]}' to show how the stack evolves and why it returns true. Also trace an invalid example like '{(})' to show early termination.

4. Analyze complexity and discuss optimizations

State that time complexity is O(n) and space complexity is O(n) in the worst case. Mention that early termination can save time for invalid strings.

5. Write clean code and test

Implement the function with clear variable names and handle edge cases. Suggest writing unit tests for various scenarios.

Key Points to Mention

Stack data structure and its LIFO property
Mapping of closing brackets to opening brackets (e.g., using a hash map)
Handling of empty string and strings with no brackets
Time and space complexity analysis (O(n) time, O(n) space)
Edge cases: unmatched brackets, incorrect order, non-bracket characters
Early termination when a mismatch is found

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.