Instacart·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Coding round at Instacart for a software engineer role. One problem, but it had layers. The wheelchair extension tripped me up more than I expected for something that looked like a straightforward OOP tweak.

Questions Asked (1)

You're given a priority boarding simulation for a bus. Extend it to support wheelchair passengers, where each wheelchair has a size that consumes general capacity in addition to occupying one of two dedicated wheelchair spots. Wheelchair passengers follow the same priority ordering rules, and if one can't fit you skip them and continue. Return the boarded list and the left-behind list.

Algorithms & Data StructuresTechnical Trade-offsSystem Design

Author's notes

I spent the first few minutes just restating the problem back, which was probably annoying.

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AI HintsAI Generated

Suggested Approach

Clarify the existing priority rules and data structures, then model wheelchair passengers as consuming both a dedicated spot and general capacity. Process passengers in priority order, attempting to board each; if a wheelchair passenger cannot fit due to either constraint, skip them and continue. Return the boarded and left-behind lists.

Pro tip: Explicitly state your assumptions about priority ordering and capacity constraints, and discuss how you'd handle edge cases like multiple wheelchairs or zero general capacity. This shows attention to detail and real-world robustness.

1. Understand the existing simulation

Review the current priority boarding logic, data structures, and how general capacity is tracked. Identify where wheelchair support needs to be integrated.

2. Define wheelchair constraints

Each wheelchair passenger requires one of two dedicated spots and also consumes general capacity equal to their size. Ensure both constraints are checked atomically.

3. Process in priority order

Iterate through passengers in the given priority order. For each, check if they can board: for wheelchair users, verify both a dedicated spot and enough general capacity; for others, only general capacity.

4. Handle skips and continue

If a passenger cannot board, add them to the left-behind list and continue to the next passenger without stopping. This ensures higher-priority passengers who can't fit don't block lower-priority ones.

5. Return results

After processing all passengers, return the boarded list (in boarding order) and the left-behind list (in original priority order).

Key Points to Mention

Priority ordering rules must be preserved for all passengers, including wheelchair users.
Wheelchair passengers consume both a dedicated spot (max 2) and general capacity equal to their size.
If a wheelchair passenger cannot fit due to either constraint, they are skipped and added to left-behind.
General capacity is a shared resource; non-wheelchair passengers only consume general capacity.
Edge cases: more than two wheelchair passengers, zero general capacity, wheelchair size larger than remaining capacity.
Time complexity: O(n) if processing in priority order with O(1) checks per passenger.

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