Jump Trading·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Jump Trading coding round, one question on array manipulation. Pretty standard stuff but the carry-propagation edge case is where people slip up if they're not careful.

Questions Asked (1)

Given an array of digits representing a non-negative integer (most significant digit first), increment the integer by one and return the resulting digit array.

Algorithms & Data Structures

Author's notes

Straightforward on the surface.

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AI HintsAI Generated

Suggested Approach

Start by clarifying edge cases like all 9s and empty array, then propose a linear time solution that traverses from the least significant digit, handling carry propagation. Discuss the trade-offs between in-place modification and creating a new array, and mention the possibility of an early exit when no carry is needed.

Pro tip: At Jump Trading, interviewers value clean, efficient code and awareness of edge cases. Emphasize that the solution runs in O(n) time and O(1) extra space (if modifying in-place), and proactively discuss how you would test it with cases like [9,9,9] and [0].

1. Clarify requirements and edge cases

Ask about input constraints (e.g., empty array, leading zeros) and expected output format. Confirm whether the array can be modified in-place or if a new array is required.

2. Outline the algorithm

Explain that you will iterate from the end of the array, adding 1 and propagating carry. If a digit is less than 9, increment it and return; if it's 9, set to 0 and continue.

3. Handle the all-9s case

If the loop completes without returning, all digits were 9, so the result is a new array with a leading 1 followed by zeros (e.g., [9,9,9] -> [1,0,0,0]).

4. Analyze complexity

State that the time complexity is O(n) in the worst case (all 9s) and O(1) in the best case (last digit < 9). Space complexity is O(1) if modifying in-place, or O(n) if creating a new array.

5. Test with examples

Walk through examples like [1,2,3] -> [1,2,4], [1,2,9] -> [1,3,0], and [9,9,9] -> [1,0,0,0] to verify correctness.

Key Points to Mention

Carry propagation logic and early termination when no carry remains
Edge cases: empty array, single element, all 9s, leading zeros
Time and space complexity analysis
In-place modification vs. creating a new array
Potential for integer overflow if converting to a number (avoid that approach)
Code clarity and modularity (e.g., separate function for increment)

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