← Chicago Interview Insights

Chicago·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026Chicago

Summary

Coding interview for a software engineer role somewhere in Chicago. One problem, iterative dictionary merging, which sounds easy until you actually think through the nested dict case without recursion.

Questions Asked (1)

Q1

Given a list of Python dictionaries, write a function that merges them into one dictionary iteratively (no recursion). Later keys override earlier ones, except when both values are dicts, in which case you merge those too.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I started confident because 'merge dicts' felt like a one-liner.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: iterative merge, later keys override, and recursive merge for nested dicts. Then outline an iterative approach using a stack to handle nested dictionaries, ensuring no recursion. Finally, discuss trade-offs like time/space complexity and edge cases.

Pro tip: Mention that using a stack avoids recursion limits and is more memory-efficient for deep nesting, but be prepared to discuss when recursion might be simpler and acceptable.

1. Clarify Requirements

Confirm that the merge should be iterative, later keys override, and nested dicts are merged recursively. Ask about input size and depth to inform approach.

2. Design Iterative Algorithm

Use a stack to simulate recursion: push pairs of dicts to merge, and process them iteratively. For each key, if both values are dicts, push them onto the stack; otherwise, override.

3. Implement and Test

Write the function, handling edge cases like empty lists, non-dict values, and deep nesting. Test with examples to ensure correctness.

4. Analyze Complexity

Discuss time complexity O(N) where N is total number of key-value pairs, and space complexity O(D) for stack depth D. Compare with recursive approach.

5. Discuss Trade-offs

Highlight pros and cons: iterative avoids recursion limit but may be more complex; recursive is simpler but risks stack overflow. Mention potential optimizations.

Key Points to Mention

  • Iterative approach using a stack to avoid recursion limits
  • Handling nested dictionaries by merging recursively (simulated iteratively)
  • Later keys override earlier ones, except when both values are dicts
  • Time and space complexity analysis
  • Edge cases: empty list, non-dict values, deep nesting
  • Trade-offs between iterative and recursive solutions

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