Google·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Google SWE coding round, one problem the whole session. Seemed straightforward at first glance but the constraints made it interesting.

Questions Asked (1)

Given an integer array and an integer k, find the maximum sum of a contiguous subarray where the absolute difference between the first and last elements equals exactly k. Return 0 if no such subarray exists.

Algorithms & Data Structures

Author's notes

My first instinct was brute force, check every pair of indices where the endpoints differ by k and track the max sum.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem constraints and edge cases. Then, propose an efficient algorithm, such as using a hash map to track prefix sums for each possible first element value, and analyze its time and space complexity. Finally, discuss potential optimizations or alternative approaches.

Pro tip: Demonstrate strong problem-solving by explicitly discussing trade-offs between different approaches (e.g., brute force vs. optimized) and mentioning how you would test the solution with edge cases like k=0 or negative numbers.

1. Clarify the problem

Ask clarifying questions about input constraints (e.g., array size, element range, negative numbers) and confirm the definition of 'absolute difference' and 'contiguous subarray'.

2. Brainstorm approaches

Start with a brute-force O(n^2) solution to establish correctness, then think about optimizations using data structures like hash maps or prefix sums.

3. Design an efficient algorithm

For each possible first element value, track the minimum prefix sum before it and the maximum subarray sum ending at each position, ensuring the last element differs by exactly k.

4. Analyze complexity

State the time and space complexity of your solution, typically O(n) time and O(n) space with a hash map, and explain why it's optimal.

5. Test with examples

Walk through a few test cases, including edge cases like no valid subarray (return 0), k=0, and arrays with negative numbers.

Key Points to Mention

Handling edge cases such as empty array, k=0, and no valid subarray
Using a hash map to store prefix sums for each possible first element value
Maintaining the maximum subarray sum for each valid pair of first and last elements
Time and space complexity analysis (O(n) time, O(n) space)
Trade-offs between brute force and optimized approaches
Potential follow-up: how to handle streaming input or large datasets

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