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Jane Street·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Jane Street software engineer interview with a coding question on evaluating a tokenized infix arithmetic expression. The problem was well-scoped but the precedence and parentheses handling had enough edge cases to keep things interesting. No fluff, just straight into the technical stuff.

Questions Asked (1)

Q1

Given an already-tokenized arithmetic expression as an array of strings (integers, operators +/-/*, /, and parentheses), evaluate it and return the integer result. Standard operator precedence and left-to-right associativity apply, and all divisions are guaranteed exact.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The 'already tokenized' part is doing a lot of work in this problem.

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AI HintsAI Generated

Suggested Approach

Use two stacks: one for operands and one for operators, processing tokens left to right while respecting precedence and parentheses. Alternatively, convert the infix expression to postfix (shunting-yard) and evaluate, or use recursive descent parsing. Clearly explain your chosen method, handle edge cases, and analyze time/space complexity.

Pro tip: At Jane Street, they value clean, efficient code and clear communication. Before coding, briefly outline your approach and discuss trade-offs (e.g., two-stack vs. recursive descent) to demonstrate strategic thinking. Also, mention that exact division simplifies handling but still consider integer overflow.

1. Clarify and Confirm

Restate the problem to ensure understanding: tokenized input, operators, parentheses, exact division. Ask about constraints (e.g., input size, integer range) if not provided.

2. Choose an Approach

Decide between two-stack evaluation, shunting-yard to postfix, or recursive descent. Consider simplicity, efficiency, and ease of handling parentheses and precedence.

3. Outline the Algorithm

Describe step-by-step how your chosen method works, including how to handle operator precedence, parentheses, and left-to-right associativity.

4. Analyze Complexity and Edge Cases

State time and space complexity (typically O(n)). Discuss edge cases: negative numbers, multi-digit integers, nested parentheses, division by zero (though guaranteed exact), and integer overflow.

5. Implement and Test

Write clean code with meaningful variable names. Walk through a simple example (e.g., ['2', '+', '3', '*', '4']) to verify correctness.

Key Points to Mention

  • Operator precedence and left-to-right associativity for same-precedence operators.
  • Handling parentheses by evaluating sub-expressions first.
  • Choice of data structures: stacks for operands and operators, or recursion for parsing.
  • Time and space complexity: O(n) time, O(n) space in worst case.
  • Edge cases: negative numbers, multi-digit integers, nested parentheses, and exact division.
  • Trade-offs between iterative (two-stack) and recursive (descent) approaches.

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