Jump Trading·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Jump Trading SWE interview with a math-flavored coding problem. Pretty focused session, just the one problem but they clearly wanted to see clean reduction logic and not just a brute force.

Questions Asked (1)

Given two arrays X and Y of the same length, where each pair X[i] and Y[i] represents a fraction, find the most frequently occurring fraction. Fractions that reduce to the same lowest terms count as the same. Return the count of the most common one.

Algorithms & Data Structures

Author's notes

My first instinct was to just stringify the numerator and denominator and use that as a key, which would've broken on equivalent fractions like 2/3 and 4/6.

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AI HintsAI Generated

Suggested Approach

Normalize each fraction by dividing numerator and denominator by their greatest common divisor, then use a hash map to count occurrences of each reduced fraction. Track the maximum count as you iterate. Discuss handling edge cases like negative fractions and zero denominators.

Pro tip: Mention that you can avoid floating-point precision issues by using integer pairs as keys, and that normalizing signs (e.g., ensuring denominator is positive) is crucial for correct grouping.

1. Clarify requirements and edge cases

Ask about input constraints: can denominators be zero? Are fractions negative? Should we return the count or the fraction itself? Confirm that reduced fractions are considered equal.

2. Design normalization strategy

For each fraction, compute the greatest common divisor (GCD) of absolute values of numerator and denominator, then divide both by it. Ensure the denominator is positive by flipping signs if needed.

3. Use a hash map for counting

Store the normalized fraction as a key (e.g., a tuple or a string) and increment its count. Keep track of the maximum count seen so far.

4. Analyze complexity and optimize

Time complexity is O(n log(min(a,b))) due to GCD per fraction, space O(n) for the map. Discuss potential optimizations like early termination if a count exceeds half the array length.

5. Test with examples

Walk through a small example, including negative fractions and reducible fractions, to verify correctness. Mention that zero fractions (0/1) are handled naturally.

Key Points to Mention

Greatest Common Divisor (GCD) for reducing fractions
Using integer pairs as hash map keys to avoid floating-point precision issues
Handling negative fractions by normalizing signs (denominator positive)
Time and space complexity analysis
Edge cases: zero denominator, zero numerator, all fractions unique
Potential follow-up: what if the arrays are very large? (streaming approach)

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