UiPath·Machine Learning Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Interviewed for an ML Engineer role at UiPath and got a coding question that felt more like a software engineering screen than anything ML-related. Classic string problem, but they wanted me to walk through multiple approaches and complexity tradeoffs, which I wasn't fully prepared for.

Questions Asked (1)

Given an array of strings, write a function that finds the longest common prefix shared by all strings. Return an empty string if none exists.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I jumped straight to the vertical scan approach (compare character by character across all strings at the same index) which works fine, but then they asked me to walk through other ways to do it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (e.g., input size, character set) and then propose a vertical scanning approach that compares characters column by column across all strings. Discuss time and space complexity, and mention alternative strategies like divide-and-conquer or binary search for trade-offs. Finally, walk through a concrete example to validate the solution.

Pro tip: Mention that in a machine learning context, this problem mirrors feature extraction where common patterns are identified across data points, and highlight that early termination can significantly optimize performance for large datasets.

1. Clarify requirements and edge cases

Ask about input size, character set, and whether the array can be empty or contain empty strings. Discuss how to handle these edge cases.

2. Propose a primary algorithm

Describe the vertical scanning approach: iterate through characters of the first string and compare with the same position in all other strings until a mismatch is found.

3. Analyze complexity and trade-offs

State that time complexity is O(S) where S is the sum of all characters, and space is O(1). Compare with horizontal scanning, divide-and-conquer, and binary search, noting when each might be preferable.

4. Walk through an example

Use a sample input like ['flower','flow','flight'] to demonstrate how the algorithm finds 'fl' and terminates early when a mismatch occurs.

5. Discuss optimizations and ML relevance

Mention early termination, and relate the problem to ML tasks like finding common features across embeddings or preprocessing text data for model training.

Key Points to Mention

Vertical scanning vs. horizontal scanning: trade-offs in early termination and worst-case performance
Time complexity O(S) and space complexity O(1), where S is the total number of characters
Handling edge cases: empty array, single string, empty strings, and strings of different lengths
Divide-and-conquer approach: recursively find LCP of left and right halves, then merge
Binary search on the length of the prefix: check if a prefix of length k is common to all strings
Relevance to ML: feature extraction, common pattern identification in data, and efficient preprocessing

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