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

IntermediatePrefer not to say

Jul 2026

Summary

Google onsite coding round, one problem the whole session with a follow-up tacked on once I had the boolean version working. The core problem looked deceptively clean but the edge cases around the removed link's position tripped me up for a bit.

Questions Asked (1)

You're given an array representing the link weights of a gold chain. Remove exactly one link, reconnect the remaining links into a chain, then check if you can make a single cut that splits the chain into two pieces of equal total weight. Return true if any valid (remove, cut) pair exists. Follow-up: return all such pairs.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

My first instinct was prefix sums, which was right, but I kept fumbling the boundary conditions.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem constraints and edge cases, then derive the necessary condition: after removing one link, the remaining total weight must be even, and there must exist a contiguous subarray (the cut piece) with weight equal to half of that total. Use prefix sums and a hash set to check for such a subarray in O(n) time, and extend the same logic to return all pairs by storing indices.

Pro tip: Mention that the removal and cut must be on distinct links, and that the cut can be at either end of the remaining chain; also note that the follow-up can be solved by storing all prefix sum indices in a hash map to retrieve all valid cuts efficiently.

1. Clarify the problem

Restate the problem in your own words, confirm that the removed link is not part of the final chain, and ask about constraints (e.g., array size, weights, duplicates).

2. Derive the condition

After removing one link, the remaining total weight must be even, and the cut must split the chain into two contiguous pieces of equal weight, meaning one piece has weight equal to half the remaining total.

3. Design an efficient algorithm

Use prefix sums and a hash set to check for a contiguous subarray with the target weight in O(n) time; for the follow-up, use a hash map from prefix sum to list of indices to collect all valid cuts.

4. Handle edge cases and validate

Consider cases where the removed link is at the beginning or end, when the remaining total is odd, and when multiple cuts yield the same piece; test with small examples.

5. Analyze trade-offs

Discuss time and space complexity: O(n) time and O(n) space for the hash-based approach, versus O(n^2) brute force; mention that the follow-up may require O(n) space to store all pairs.

Key Points to Mention

The remaining total weight after removal must be even.
The cut must produce two contiguous pieces, so we need a contiguous subarray with weight equal to half the remaining total.
Use prefix sums to compute subarray sums in O(1) time.
A hash set can check for the existence of a valid cut in O(n) time.
For the follow-up, a hash map from prefix sum to list of indices can retrieve all valid cuts.
Edge cases: removal at ends, odd total, multiple valid cuts, and ensuring the removed link is not part of the cut piece.

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