Software Engineer · Phone Screen · Coding

Confluent — Software Engineer

Level: Junior-Level

Round: Phone Screen · Type: Coding · Difficulty: 7/10 · Duration: 60 min · Interviewer: Neutral

Topics: Data Structures, Algorithms, Heap, Priority Queue

Location: San Francisco Bay Area

Interview date: 2025-12-28

Summary

I was asked to implement a pod management system with add, increment, and remove operations based on load. The problem involved maintaining pods and their loads, handling global increments, and efficiently removing the pod with the minimum load.

Details

The coding question I received was:

You are given a list logs of events for a system of “pods.” Each event is a pair [status, load]:

• status == 1: Add a new pod with initial load load.
• status == 2: Increase the load of every existing pod by load (a global increment).
• status == 3: Remove the pod with the smallest current load and record/output its current load.

Return a list of the loads produced by every status == 3 operation, in order.

Example input format: logs = [[1, 5], [1, 2], [2, 3], [3, 0], [3, 0]]

Meaning: add pod(5), add pod(2), add +3 to all, pop min → outputs 5, pop min → outputs 8 (After +3: loads are 8 and 5; min is 5, then 8)

My approach:

1. I used a min-heap (priority queue) to keep track of the pods and their loads.
2. When adding a pod (status == 1), I added it to the heap.
3. When incrementing the load of all pods (status == 2), I maintained a global increment value and updated each pod's actual load when it was accessed from the heap.
4. When removing the pod with the smallest load (status == 3), I retrieved the minimum element from the heap, adjusted its load by subtracting the global increment, and added it to the result.

Key insights:

• Using a min-heap allows efficient retrieval of the pod with the smallest load.
• Maintaining a global increment avoids updating all pod loads on each increment operation, optimizing performance.
• Adjusting the load when accessing elements from the heap ensures the correct load is used for comparisons and removal.