Microsoft·Machine Learning Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Coding round for an ML Engineer role at Microsoft. One algorithm problem, no behavioral, pretty short. Left feeling unsure about how it went.

Questions Asked (1)

Given an integer array and an integer k, determine if the array has a continuous subarray of size at least two whose elements sum up to a multiple of k.

Algorithms & Data Structures

Author's notes

Went in blind on this one and just coded up the brute force.

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AI HintsAI Generated

Suggested Approach

Use prefix sums and modular arithmetic: compute cumulative sums modulo k and track the first index where each remainder appears. If the same remainder appears at two indices at least two apart, the subarray between them sums to a multiple of k.

Pro tip: Handle edge cases like k=0 or negative numbers by using modulo normalization, and mention that the algorithm runs in O(n) time with O(min(n, k)) space, which is optimal for large inputs.

1. Clarify the problem and constraints

Confirm that the subarray must have size at least 2, and discuss edge cases such as k=0, negative numbers, and large arrays. This shows attention to detail.

2. Explain the prefix sum modulo idea

Describe how the sum of a subarray from i+1 to j is (prefix[j] - prefix[i]) mod k. If this is 0, then prefix[j] ≡ prefix[i] (mod k).

3. Outline the algorithm

Iterate through the array, compute the running sum modulo k, and store the first index for each remainder in a hash map. If a remainder repeats and the index difference is at least 2, return true.

4. Analyze complexity and edge cases

State that time complexity is O(n) and space is O(min(n, k)). Mention handling k=0 separately (check for two consecutive zeros) and normalizing negative remainders.

5. Provide a code example or pseudocode

Walk through a simple example like [23,2,4,6,7], k=6 to illustrate the approach, and optionally write concise pseudocode.

Key Points to Mention

Prefix sums and modular arithmetic
Hash map to store first occurrence of each remainder
Condition for subarray length ≥ 2
Time complexity O(n) and space complexity O(min(n, k))
Edge cases: k=0, negative numbers, empty array
Normalization of negative remainders using (sum % k + k) % k

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