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

Intermediate

May 2026

Summary

Google SWE interview with a simulation/algorithm question that had a deceptively tricky tie-breaking system. Got through the logic but ran out of time before a clean dry-run, and the interviewer caught a couple bugs.

Questions Asked (1)

You're given a sorted array where each index represents a person and each value is a tuple of (timestamp, 'enter' or 'exit'). Return an array where each index is a person and each value is the time they actually enter or exit, after applying tie-breaking rules: if the previous moment had an enter, enters get priority; if it had an exit, exits get priority; if nothing happened, exits get priority; and for simultaneous actions, lower index goes first.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The tie-breaking rules are where this gets messy.

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AI HintsAI Generated

Suggested Approach

Clarify the problem by restating the tie-breaking rules and walking through a small example to ensure alignment. Then propose an event-driven simulation that processes actions in chronological order, applying the priority rules at each timestamp, and finally outputs the resolved times. Discuss time and space complexity, and consider edge cases like multiple actions at the same timestamp.

Pro tip: Demonstrate proactive communication by explicitly stating your assumptions about the input format and tie-breaking rules before diving into the solution. This shows attention to detail and reduces the risk of solving the wrong problem.

1. Clarify requirements and constraints

Ask questions to confirm the input format, output format, and exact tie-breaking rules. For example, confirm that each person has exactly one enter and one exit, and that timestamps are integers.

2. Design an event-driven simulation

Collect all actions (enter/exit) with their timestamps and person indices. Sort them by timestamp, then by priority rules (based on previous moment's action and index). Process in order, resolving simultaneous actions according to the rules.

3. Implement priority logic

For each timestamp, group actions. Determine the priority order: if the previous moment had an enter, enters first; if exit, exits first; if nothing, exits first. Within same type, lower index first. Assign the actual time (the timestamp) to each person's action.

4. Handle edge cases and validate

Consider cases like multiple enters/exits at the same timestamp, first timestamp with no previous action, and ensure the output array is correctly indexed by person. Walk through a small example to verify.

5. Analyze complexity and optimize

Discuss time complexity (O(N log N) due to sorting) and space complexity (O(N)). Mention potential optimizations if the input is already sorted by timestamp, or if we can use counting sort for integer timestamps.

Key Points to Mention

Event-driven simulation: process actions in chronological order, applying tie-breaking rules at each timestamp.
Priority rules: depends on previous moment's action (enter/exit/none) and index order for simultaneous actions.
Data structures: use a list of events (timestamp, type, index) and sort by timestamp, then custom comparator for priority.
Edge cases: first timestamp, multiple actions at same timestamp, all enters or all exits at a timestamp.
Time and space complexity: O(N log N) time, O(N) space; mention if input is already sorted, can be O(N).
Output format: array where each index corresponds to a person, value is the resolved time.

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