Instacart·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Coding screen for a software engineer role at Instacart. One algorithmic string manipulation question, pretty focused, nothing too wild but it had a few edge cases that could trip you up if you rushed.

Questions Asked (1)

Given an array of strings, for each string check if both the first and last characters are vowels (case-insensitive). If they are, reverse everything between the first and last characters and return the modified array. If not, leave the string as-is.

Algorithms & Data Structures

Author's notes

Took me a minute to realize 'middle portion' meant indices 1 through len-2, not some fuzzy definition.

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AI HintsAI Generated

Suggested Approach

Clarify edge cases and constraints first, then outline a single-pass solution that checks each string's first and last characters for vowels. For qualifying strings, reverse the substring between the first and last characters using two pointers or slicing, and build the result array.

Pro tip: Mention that you would handle empty strings and single-character strings gracefully, and note that reversing the middle can be done in-place to save space if the input array is mutable.

1. Clarify requirements and edge cases

Ask about input constraints (e.g., string length, character set), whether the array can be modified in-place, and how to handle empty or single-character strings.

2. Define vowel check and identify qualifying strings

Create a helper function to check if a character is a vowel (case-insensitive). For each string, check if both first and last characters are vowels.

3. Reverse the middle substring for qualifying strings

If the string qualifies, reverse the substring between the first and last characters (exclusive). Use two pointers or slicing, ensuring not to reverse the first and last characters themselves.

4. Build and return the modified array

Collect the modified strings into a new array or modify the original array in-place, then return it.

5. Test with examples and edge cases

Walk through examples like ['apple', 'banana', 'aeiou'] and edge cases like empty strings, single characters, and non-vowel boundaries to verify correctness.

Key Points to Mention

Case-insensitive vowel check (a, e, i, o, u)
Handling empty strings and single-character strings (no reversal needed)
Reversing only the substring between first and last characters, not including them
Time complexity: O(n) where n is total characters; space complexity: O(1) extra if in-place
Using two pointers or slicing for reversal
In-place modification vs. creating a new array

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