Uber·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Uber Data Scientist coding round, basically one array manipulation problem with a follow-up that tightened the constraints. Not the most grueling session but the edge cases will bite you if you're not careful.

Questions Asked (1)

Given an array, rotate it by k positions. Walk through your approach, then redo it under tighter memory constraints (O(1) extra space).

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

First pass I just reached for a temp array and it worked fine, but then they asked me to do it without allocating extra space and I stalled a bit.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the rotation direction and handling edge cases like k >= n. For the initial solution, use an auxiliary array to place each element at its new index, then for O(1) space, use the reversal algorithm: reverse the entire array, then reverse the first k elements and the remaining n-k elements. Walk through both approaches with a small example, and discuss trade-offs like time complexity and code simplicity.

Pro tip: Mention that the reversal method is optimal for in-place rotation, but if multiple rotations are needed, consider using a circular buffer or index mapping to avoid repeated O(n) operations. Also, clarify whether k can be negative or larger than n, as this shows attention to detail.

1. Clarify requirements and edge cases

Ask about rotation direction (left or right), whether k can be larger than array length, and if the array can be modified in-place. Handle edge cases like empty array, k=0, or k multiple of n.

2. Present the auxiliary array approach

Explain that you can create a new array and place each element at index (i+k) % n. This is O(n) time and O(n) space, simple and easy to understand.

3. Introduce the O(1) space reversal algorithm

Describe the three-step reversal: reverse the entire array, then reverse the first k elements, then reverse the remaining n-k elements. This achieves O(n) time and O(1) extra space.

4. Walk through an example

Use a small array like [1,2,3,4,5] with k=2 to demonstrate both approaches, showing the intermediate steps of the reversal method.

5. Discuss trade-offs and alternatives

Compare time and space complexity, code readability, and potential pitfalls. Mention other methods like cyclic replacements or using a temporary variable for one-by-one rotation, and when they might be preferable.

Key Points to Mention

Time complexity: O(n) for both approaches, but auxiliary array uses O(n) extra space while reversal uses O(1).
Edge cases: k=0, k>=n, empty array, and negative k (if allowed).
Rotation direction: left vs right, and how to adjust k accordingly (e.g., k = k % n).
Reversal algorithm steps: reverse whole, reverse first k, reverse rest.
Alternative in-place methods: cyclic replacements (juggling algorithm) and its complexity.
Practical considerations: readability, potential for off-by-one errors, and whether the array is mutable.

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