Meta·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Meta coding round, one question the whole time. It's a string parsing problem that looks deceptively manageable until you're actually writing the recursive logic under pressure.

Questions Asked (1)

Given a string encoding of a binary tree where each node is its value followed by optional parenthesized left and right subtrees, parse the string and construct the actual tree. Handle single nodes, multi-digit values, and missing right children.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I got the basic structure pretty fast but the index tracking killed me.

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AI HintsAI Generated

Suggested Approach

Use a recursive descent parser with an index pointer to parse the string. At each node, parse the integer value, then if the next character is '(', recursively parse the left subtree, and if another '(' follows, parse the right subtree. Return the constructed node and advance the index accordingly.

Pro tip: Clarify the exact grammar and edge cases (e.g., empty string, spaces, negative numbers) before coding, and mention that you'll write a helper function to parse the integer to handle multi-digit values robustly.

1. Clarify the grammar and constraints

Ask about the exact format: are values always non-negative integers? Can there be spaces? What about empty strings? Confirm that missing right child is represented by omitting the second parentheses group.

2. Design the recursive parser

Outline a function that takes the string and a mutable index (or uses a class member). It parses the value, then checks for '(' to parse left and right subtrees recursively.

3. Handle multi-digit values and edge cases

Write a helper to parse consecutive digits into an integer. Ensure that after parsing a subtree, the closing ')' is consumed. Handle cases where only left child exists (e.g., '1(2)') and no children (e.g., '1').

4. Implement and test with examples

Code the solution, then walk through examples like '1(2)(3)', '4(2(3)(1))(6(5))', and '1(2)' to verify correctness. Discuss time and space complexity.

5. Discuss trade-offs and optimizations

Mention that recursion depth could be an issue for skewed trees; consider iterative approach with stack if needed. Also discuss error handling for malformed input.

Key Points to Mention

Recursive descent parsing with an index pointer to avoid string slicing overhead.
Handling multi-digit numbers by accumulating digits until a non-digit character.
Distinguishing between missing left child and missing right child: if after parsing value the next char is '(', it's left child; after parsing left, if next char is '(', it's right child.
Consuming closing parentheses correctly to maintain index position.
Time complexity O(n) where n is the length of the string, and space complexity O(h) for recursion stack (h = tree height).
Edge cases: empty string, single node, only left child, negative numbers (if allowed), and whitespace handling.

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