Carvana·Backend Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Did a technical phone screen for a backend role at Carvana and got a number-to-English conversion problem. Managed to code up the under-1000 case but kind of stalled out when it came to the larger numbers and just talked through the rest.

Questions Asked (1)

Given an integer, write a function that converts it to its English words representation (e.g. 1234 becomes "One Thousand Two Hundred Thirty Four").

Algorithms & Data Structures

Author's notes

Got the sub-1000 logic coded up fine, chunks of hundreds, tens, ones, no problem.

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AI HintsAI Generated

Suggested Approach

Break the problem into recursive chunks: handle numbers below 1000, then scale by thousands, millions, and billions. Use arrays for words of ones, teens, and tens, and a helper function to convert any three-digit group. Concatenate results with appropriate scale words and handle edge cases like zero and negative numbers.

Pro tip: Mention that you'd clarify requirements first: range of integers (e.g., 32-bit vs 64-bit), handling of zero, negatives, and whether to include 'and' (e.g., 'One Hundred and Twenty Three'). This shows attention to detail and prevents rework.

1. Clarify requirements and edge cases

Ask about input range, negative numbers, zero, and formatting conventions (e.g., use of 'and', capitalization). Confirm expected output for edge cases like 0, 100, 1000, and 1,000,000.

2. Define word mappings and helper function

Create arrays for ones (1-19), tens (20-90), and scale words (Thousand, Million, Billion). Write a helper function to convert any number less than 1000 into words.

3. Process number in groups of three digits

Iterate through the number from least significant to most significant, extracting three-digit chunks. For each chunk, convert to words using the helper and append the appropriate scale word.

4. Handle special cases and assemble result

Handle zero separately. For negatives, prepend 'Minus'. Join the word groups with spaces, ensuring no extra spaces and proper capitalization.

5. Test with representative cases

Walk through examples like 0, 5, 21, 100, 1234, 1000000, and negative numbers to verify correctness. Discuss time and space complexity.

Key Points to Mention

Modular design: separate logic for numbers <1000 and scaling by thousands/millions/billions.
Use of arrays for word mappings (ones, teens, tens) to avoid hardcoding many conditionals.
Handling of edge cases: zero, negative numbers, and numbers with internal zeros (e.g., 1001).
Time and space complexity: O(n) where n is the number of digits, with constant extra space for word arrays.
Potential pitfalls: incorrect pluralization (e.g., 'One Hundred' vs 'One Hundreds'), missing spaces, and handling of 'and' in British English.
Testing strategy: unit tests for boundary values and random numbers, comparing against known outputs.

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