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intercontinental exchange·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026

Summary

A coding round for a Software Engineer role at Intercontinental Exchange. Thirty minutes, one array problem, C++ only. Pretty focused and no-nonsense.

Questions Asked (1)

Q1

Solve an array problem using a hash map and sorting in C++. Walk through your approach including how you're using the map, your sorting strategy (e.g. sorting by value while preserving stable order), and the time and space complexity.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Python wasn't allowed which tripped me up a bit since I default to it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and constraints, then outline a solution that uses a hash map to store frequencies or indices, followed by sorting based on values while preserving stable order. Walk through the algorithm step-by-step, analyze time and space complexity, and discuss trade-offs such as when to use a map versus other data structures.

Pro tip: Mention that std::sort is not stable, so if stable order is required, use std::stable_sort or sort pairs with the original index as a tiebreaker. This shows attention to detail and understanding of C++ standard library nuances.

1. Clarify the problem and constraints

Ask clarifying questions to understand the input array, expected output, and any constraints (e.g., duplicates, order preservation). This ensures you address the correct problem.

2. Design the hash map usage

Explain how you'll use a hash map (e.g., std::unordered_map) to store frequencies, indices, or other relevant data. Discuss why a hash map is suitable (O(1) average lookup/insertion).

3. Plan the sorting strategy

Describe how you'll sort the elements, specifying the sorting criterion (e.g., by value) and how you'll preserve stable order if needed (e.g., using std::stable_sort or storing original indices).

4. Analyze complexity and trade-offs

State the time and space complexity of your approach, and discuss alternative strategies (e.g., using a map vs. sorting first) and their trade-offs.

5. Walk through an example

Trace your algorithm on a small example to demonstrate correctness and clarify any edge cases.

Key Points to Mention

  • Choice of hash map (std::unordered_map) and its average O(1) operations
  • Sorting algorithm: std::sort (O(n log n)) vs. std::stable_sort for stability
  • Preserving original order: using indices or stable_sort
  • Time complexity: O(n log n) due to sorting, space complexity: O(n) for the map
  • Trade-offs: when to use a map vs. sorting first (e.g., if multiple queries)
  • Edge cases: empty array, all duplicates, negative numbers

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