DoorDash·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026Remote

Summary

DoorDash coding round centered on a buggy implementation problem, specifically around their dasher order-selection logic. The whole thing was about finding subtle off-by-one errors in index handling, which sounds easy until you're staring at it under pressure.

Questions Asked (1)

You're given a buggy implementation of a delivery driver order-selection routine. Find and fix the bugs, paying close attention to index handling during removal operations, and walk through the corrected logic with example inputs.

Algorithms & Data StructuresRoot Cause AnalysisTechnical Trade-offs

Author's notes

The sneaky part was the remove call.

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AI HintsAI Generated

Suggested Approach

First, restate the problem and clarify the expected behavior of the order-selection routine. Then, systematically trace through the code with a small example to identify bugs, focusing on index handling during removal. Finally, explain the fixes and validate with additional test cases, discussing trade-offs.

Pro tip: When removing elements from a list while iterating, always iterate backwards or use a while loop with manual index control to avoid skipping elements. Also, consider edge cases like empty lists or removing the last element.

1. Understand the problem and expected behavior

Restate the routine's purpose: selecting orders for a delivery driver based on some criteria. Clarify input/output and any constraints.

2. Identify and analyze the buggy code

Walk through the code line by line, paying special attention to loops and removal operations. Use a small example to trace execution and spot index issues.

3. Fix the bugs and explain the corrections

Propose fixes, such as iterating backwards or adjusting indices after removal. Explain why each fix resolves the issue.

4. Validate with example inputs

Test the corrected routine with multiple examples, including edge cases, to ensure it works as expected.

5. Discuss trade-offs and alternative approaches

Mention any performance implications or alternative data structures (e.g., using a new list) and their trade-offs.

Key Points to Mention

Index out-of-bounds or skipping elements due to forward iteration during removal
Using a while loop with manual index control or iterating backwards
Edge cases: empty list, single element, removing all elements
Time and space complexity of the fix
Alternative: build a new list with elements to keep
Importance of clear variable naming and code readability

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