Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Meta SWE interview, came across a coding question that was straight off LeetCode. Not much else to go on but it was a technical screen of some kind.

Questions Asked (1)

Given an integer array and an integer k, determine whether the array has a continuous subarray of at least two elements whose sum is a multiple of k (LeetCode 523).

Algorithms & Data Structures

Author's notes

Prefix sum with modulo arithmetic.

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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 again at least two indices apart, a subarray with sum divisible by k exists.

Pro tip: Handle edge cases like k=0 and negative numbers by normalizing remainders; also mention that the subarray must have length at least 2, so check index difference > 1.

1. Understand the problem

Clarify that we need a continuous subarray of length >= 2 whose sum is a multiple of k. Note that k can be negative or zero, and array elements can be negative.

2. Use prefix sums and remainders

Compute prefix sums modulo k. If two prefix sums have the same remainder, the subarray between them has sum divisible by k.

3. Track first occurrence of each remainder

Use a hash map to store the earliest index for each remainder. Initialize with remainder 0 at index -1 to handle subarrays starting at index 0.

4. Check for valid subarray length

When a remainder repeats, check if the current index minus the stored index is at least 2. If so, return true.

5. Handle edge cases and return result

If k=0, check for any zero-sum subarray of length >=2. Normalize negative remainders by adding k. Return false if no valid subarray found.

Key Points to Mention

Prefix sum modulo k: if two prefix sums have the same remainder, the subarray sum is divisible by k.
Hash map to store the first index of each remainder for O(n) time complexity.
Initialization with remainder 0 at index -1 to handle subarrays starting at index 0.
Ensure subarray length >= 2 by checking index difference > 1.
Handle negative numbers by normalizing remainders: (sum % k + k) % k.
Edge case k=0: need to check for zero-sum subarray of length >=2 separately.

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