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Capital One·Software Engineer·Technical Phone Screen·Senior

Senior
May 2026

Summary

Capital One Research Engineer interview with a simulation-style coding problem. The question was more involved than I expected for a phone screen, lots of edge cases hiding in plain sight.

Questions Asked (1)

Q1

Simulate warehouse operations given initial capacities. Operations are either delivering a package (assign to first available warehouse starting from index 0, cycling through) or disabling a warehouse. If no warehouse has capacity, reset all to initial values and retry. Track packages processed per warehouse and return the index with the highest count, breaking ties by picking the largest index.

Algorithms & Data StructuresSystem Design
Author's notes

I spent way too long on the cycling logic and missed the tie-breaking rule until near the end.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases first, then outline a simulation approach using a circular pointer and a capacity array. Discuss data structures for efficient warehouse selection and reset handling, and analyze time/space complexity.

Pro tip: Mention that you would confirm the reset behavior: when no warehouse has capacity, reset all capacities to initial values and retry the same operation, ensuring no infinite loop by checking if any warehouse has initial capacity > 0.

1. Clarify Requirements and Edge Cases

Ask questions to confirm: initial capacities, whether disabling is permanent, reset behavior, and tie-breaking rules. Identify edge cases like all capacities zero, disabling already disabled warehouse, and multiple resets.

2. Design Data Structures

Use an array to store current capacities and another for initial capacities. Maintain a pointer to the next warehouse to check, and a count array for packages processed. Consider a set or boolean array for disabled warehouses.

3. Simulate Operations

For each operation: if deliver, find first available warehouse with capacity > 0 by cycling from pointer; if none, reset capacities and retry. If disable, mark warehouse as disabled. Update counts and pointer accordingly.

4. Handle Reset and Retry

When no capacity, reset all non-disabled warehouses to initial capacities. If after reset still no capacity (e.g., all disabled or initial zero), the operation cannot be processed; handle gracefully.

5. Compute Result and Analyze Complexity

After all operations, find index with max count, breaking ties by largest index. Discuss time complexity: O(m * n) worst-case due to scanning, but can optimize with a queue of available warehouses.

Key Points to Mention

  • Use a circular pointer to efficiently find the next available warehouse without restarting from index 0 each time.
  • Maintain separate arrays for current and initial capacities to handle resets.
  • Track disabled warehouses to skip them during selection and reset.
  • Handle the case where reset does not help (e.g., all warehouses disabled or initial capacity zero) to avoid infinite loops.
  • Optimize by using a queue or linked list of available warehouses to reduce search time to O(1) per operation.
  • Clearly explain tie-breaking: when multiple warehouses have the same max count, return the one with the largest index.

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