Meta·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Meta data engineer screen, just one coding question the whole time. Pretty focused on string manipulation and frequency counting, which I wasn't expecting to be the entire interview.

Questions Asked (1)

Given two strings, one original and one a partial or misspelled version, return the count of letters that need to be added to the second string so that some rearrangement of it could spell the first. Case-insensitive, multiplicities count.

Algorithms & Data Structures

Author's notes

My first instinct was to sort both strings and diff them, which would've been fine but they nudged me toward O(n).

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AI HintsAI Generated

Suggested Approach

Clarify that the problem reduces to finding the difference in character frequencies between the two strings, after normalizing case. Then compute the sum of positive differences (original minus second) to get the number of letters to add.

Pro tip: Mention that you can solve it in O(n) time with a single frequency array, and that you should handle edge cases like empty strings or non-alphabetic characters if applicable.

1. Clarify the problem

Confirm that 'letters to be added' means characters missing from the second string to match the first's multiset, and that rearrangement is allowed. Ask about case sensitivity and character set.

2. Normalize inputs

Convert both strings to the same case (e.g., lowercase) to ensure case-insensitive comparison.

3. Count frequencies

Build frequency maps (or arrays) for both strings, counting each character's occurrences.

4. Compute differences

For each character in the original, compute max(0, original_count - second_count) and sum these values. This sum is the number of letters to add.

5. Return result

Return the computed sum as the answer. Optionally, discuss time and space complexity.

Key Points to Mention

Frequency counting using hash map or fixed-size array (e.g., 26 for lowercase English letters).
Case-insensitive handling by converting to lowercase or uppercase.
Multiplicity: each occurrence matters, so counts are compared directly.
Time complexity O(n + m) and space complexity O(1) if using fixed alphabet.
Edge cases: empty strings, strings with different lengths, characters not in original.
The problem is equivalent to finding the multiset difference between the two strings.

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