Glean·Software Engineer·Technical Phone Screen·Senior

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Jun 2026Remote

Summary

Glean coding round, one question the whole time, and it was one of those problems that looks manageable until you actually have to implement it cleanly under pressure. The scheduling logic wasn't hard to reason about but the implementation details piled up fast.

Questions Asked (1)

Build a priority-based job scheduler that processes a stream of jobs with arrival times, durations, and priorities. The processor runs jobs to completion without preemption, picking the highest-priority available job at each step. Ties go to the job that arrived earliest. Return each job's start time, finish time, and wait time.

Algorithms & Data StructuresSystem Design

Author's notes

I knew I needed a min-heap and figured out the key ordering pretty quickly (-priority, arrival_time).

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose an event-driven simulation using a min-heap keyed by priority and arrival time. Walk through the algorithm step-by-step, analyze time and space complexity, and discuss how to handle ties and idle periods.

Pro tip: Explicitly define the tie-breaking rule and how you handle the processor being idle when no jobs are available; this shows attention to detail and prevents off-by-one errors in start times.

1. Clarify Requirements and Edge Cases

Ask about input format, job arrival order, priority scale, tie-breaking, and whether the processor can be idle. Confirm output format and any constraints on time or memory.

2. Choose Data Structures

Use a min-heap (priority queue) to select the highest-priority job, with a custom comparator that breaks ties by earliest arrival time. Maintain a list of jobs sorted by arrival time for efficient insertion.

3. Simulate the Scheduler

Iterate through time or events: add all jobs that have arrived to the heap, then if the processor is free and the heap is non-empty, pop the top job, compute its start, finish, and wait times, and advance the current time.

4. Handle Idle and Completion

If the heap is empty and no jobs have arrived, advance time to the next arrival. After processing all jobs, ensure all jobs are scheduled and output the results.

5. Analyze Complexity and Test

State that each job is inserted and removed from the heap once, giving O(n log n) time and O(n) space. Walk through a small example to verify correctness, including ties and idle periods.

Key Points to Mention

Use a priority queue (min-heap) with a comparator that orders by priority (higher first) and then by arrival time (earlier first).
Simulate time using an event-driven approach: process jobs as they arrive and when the processor becomes free.
Compute wait time as start_time - arrival_time, and ensure finish_time = start_time + duration.
Handle the case where the processor is idle by advancing time to the next job arrival.
Time complexity: O(n log n) due to heap operations; space complexity: O(n) for storing jobs and heap.
Discuss potential variations: preemption, multiple processors, or dynamic priorities.

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