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Google·Software Engineer·Onsite - Coding / Algorithms·Senior

SeniorPrefer not to say
Jun 2026

Summary

Google SWE coding round with a chain-splitting problem that looks deceptively clean until you start thinking about the follow-up. The core question is manageable but the extension tripped me up a bit.

Questions Asked (1)

Q1

You have an array of link weights representing a golden chain. Remove exactly one link, reconnect the two remaining segments into a single chain, then make one cut to split it into two pieces of equal total weight. Return true if any valid removal index exists, false otherwise. Follow-up: return all valid (removal index, cut position) pairs.

Algorithms & Data Structures
Author's notes

The base case clicked pretty fast once I realized removing a link and reconnecting is just prefix sums on the modified array.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem constraints and edge cases. Then, derive an efficient algorithm using prefix sums and a hash map to track possible removal and cut positions. Finally, discuss time and space complexity and how to extend to the follow-up.

Pro tip: Mention that the total weight after removal must be even, and that the cut must split the reconnected chain into two contiguous segments. This shows you understand the core invariant and can quickly prune invalid cases.

1. Clarify and Restate

Confirm the problem: remove one link, reconnect the two segments, then make one cut to split into two equal-weight pieces. Ask about constraints (e.g., array size, weight values) and edge cases (e.g., all zeros, negative weights).

2. Brute Force Baseline

Describe a naive O(n^2) approach: for each removal index, compute the reconnected chain and check all possible cut positions. This establishes correctness and helps identify inefficiencies.

3. Optimize with Prefix Sums

Use prefix sums to compute segment weights in O(1). For each removal, the reconnected chain is the concatenation of two segments; the cut must split it into two equal halves. Track possible cut positions using a hash set of prefix sums.

4. Handle the Follow-up

To return all valid pairs, store removal indices and cut positions in a list. Ensure no duplicates and consider the order of removal and cut (cut can be before or after the removal point in the original array).

5. Analyze Complexity

State time and space complexity: O(n) time with O(n) space using prefix sums and hash maps. Discuss trade-offs and potential optimizations for large inputs.

Key Points to Mention

  • Total weight after removal must be even; otherwise, no valid cut exists.
  • The cut must split the reconnected chain into two contiguous segments of equal weight.
  • Use prefix sums to compute segment weights in O(1) and a hash map to track possible cut positions.
  • Consider edge cases: removal at ends, all weights zero, negative weights (if allowed), and multiple valid pairs.
  • For the follow-up, ensure all valid (removal index, cut position) pairs are returned without duplicates.
  • Time complexity: O(n) with O(n) space; explain why brute force is O(n^2).

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