TikTok·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

TikTok software engineer interview with a string chunking problem that had two parts, the second of which was genuinely tricky. The easy part felt routine but part two had a circular dependency that took me a while to untangle.

Questions Asked (1)

Given a string and a width, split the string into chunks while preserving order, then append a suffix like '1/3', '2/3', etc. to each chunk. In part one, the suffix doesn't count toward the width. In part two, it does, and you don't know the total number of chunks upfront since the suffix length depends on it. Design an algorithm that handles both cases, covers edge cases, and explain complexity.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

Part one was fine, just divide the string into slices of size w and slap the suffix on.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints and edge cases, then present a two-part solution: first, a straightforward chunking with fixed width and suffix appended afterward; second, an iterative approach that adjusts chunk size based on the suffix length, which depends on the total number of chunks. Finally, analyze time and space complexity for both parts and discuss potential optimizations.

Pro tip: Mention that in part two, the suffix length changes as the total chunk count grows, so you can solve it by iterating until the chunk count stabilizes, or by using a mathematical approach to compute the final chunk size directly. This shows you understand the circular dependency and can handle it efficiently.

1. Clarify requirements and edge cases

Ask about string length, width constraints, suffix format, and edge cases like empty string, width smaller than suffix, or width zero. Confirm that order must be preserved and chunks should be as equal as possible.

2. Solve part one: suffix not counted in width

Split the string into chunks of exactly the given width, then append the suffix 'i/n' to each chunk. The total number of chunks n is ceil(len(string)/width). This is straightforward and O(n) time.

3. Solve part two: suffix counts toward width

The suffix length depends on n, which depends on the chunk size. Use an iterative approach: start with an estimated chunk size, compute n, then recompute chunk size as width - len(suffix), and repeat until n stabilizes. Alternatively, derive a formula to compute n directly.

4. Analyze complexity and trade-offs

For part one, time O(n) and space O(n). For part two, the iterative approach converges quickly (usually 1-2 iterations), so time O(n) and space O(n). Discuss potential optimizations like precomputing suffix lengths or using binary search.

5. Test with examples and edge cases

Walk through examples like string='abcdef', width=3, and edge cases like empty string, width=1, or width smaller than suffix length. Verify that chunks are correctly sized and suffixes are accurate.

Key Points to Mention

Handling the circular dependency in part two by iterating until the number of chunks stabilizes.
Edge cases: empty string, width <= 0, width smaller than suffix length, and very long strings.
Time and space complexity analysis for both parts, emphasizing O(n) time and space.
Trade-offs between iterative and mathematical solutions for part two.
Ensuring chunks preserve order and are as equal as possible in length.
Potential optimizations: precomputing suffix lengths, using binary search to find n, or caching results.

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