TikTok·Software Engineer·Technical Phone Screen·Senior

Senior

May 2026

Summary

TikTok software engineering interview with a tricky string segmentation problem that had two parts, the second of which had a circular dependency baked into it that made things genuinely hard to reason about under pressure.

Questions Asked (2)

Given a message string and a width W, split the message into consecutive chunks of at most W characters each, then append a positional suffix like '1/3', '2/3', etc. to each chunk. The suffix does not count toward the width limit. Return the list of labeled segments.

Algorithms & Data Structures

Author's notes

Part A was fine, pretty mechanical.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: the suffix format, whether the message can be empty, and if the suffix length affects the chunk size. Then, outline a two-pass approach: first compute the total number of chunks, then split the message into chunks of size W and append the appropriate suffix.

Pro tip: Mention that you would handle edge cases like empty message, width <= 0, and very long messages that produce suffixes with more digits (e.g., '10/10') to show attention to detail.

1. Clarify requirements

Ask about the exact suffix format, whether the message can be empty, and if the width W can be zero or negative. Confirm that the suffix does not count toward the width limit.

2. Compute total chunks

Calculate the number of chunks as ceil(len(message) / W). This determines the denominator in the suffix (e.g., '1/3').

3. Split and label

Iterate through the message in steps of W, extract each chunk, and append the suffix 'i/total' where i is the 1-based chunk index.

4. Handle edge cases

If the message is empty, return an empty list or a single chunk with '1/1' depending on requirements. If W <= 0, handle gracefully (e.g., return empty list or throw error).

5. Analyze complexity

State that the time complexity is O(n) where n is the message length, and space complexity is O(n) for the output. Mention that the suffix length grows logarithmically with the number of chunks.

Key Points to Mention

Edge cases: empty message, W <= 0, message length exactly divisible by W
Suffix format: 'i/total' where i is 1-based index and total is the number of chunks
Two-pass approach: first compute total chunks, then split and label
Time and space complexity analysis
Handling large messages: suffix length may increase (e.g., '10/10') but does not affect chunk size
Potential follow-up: what if the suffix must be included in the width? Then the problem becomes more complex and may require dynamic programming.

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

Now modify the segmentation so the suffix IS included in the width limit. Since the number of segments affects the suffix length, and the suffix length affects how many segments you need, how do you resolve this circular dependency and find a valid segmentation efficiently? What's the complexity?

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

This is where I got a bit stuck.

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AI HintsAI Generated

Suggested Approach

Break the circular dependency by recognizing that the suffix length is a function of the number of segments, and the number of segments must satisfy the width constraint. Use binary search on the number of segments or iterate over possible segment counts, checking feasibility in O(1) or O(log n) per count, leading to O(log n) or O(n) overall.

Pro tip: Mention that the suffix length typically grows logarithmically with the number of segments (e.g., for a base-10 counter), so the search space is small; you can often just iterate from 1 to O(log n) segments.

1. Define the relationship

Express suffix length as a function of segment count k, e.g., suffix = '[' + str(k) + '/' + str(total) + ']' or similar, and note that total segments may be unknown initially.

2. Formulate feasibility condition

For a given k, compute the suffix length, then check if the remaining width (limit - suffix length) can be divided into k segments each of length at least 1 (or some minimum).

3. Resolve circularity

Since suffix length depends on k, but k must satisfy the width constraint, use binary search on k (if monotonic) or iterate over plausible k values (e.g., up to O(log n) or O(sqrt(n))).

4. Find valid segmentation

Once a feasible k is found, distribute the remaining width among k segments, ensuring each segment has at least the minimum length, and construct the actual segmentation.

5. Analyze complexity

State the time complexity: O(log n) if binary search, or O(log n) iterations if suffix length grows logarithmically, plus O(k) to construct the segmentation, which is O(log n) or O(n) depending on constraints.

Key Points to Mention

Monotonicity: feasibility is monotonic in k (if k works, larger k may not), enabling binary search.
Suffix length growth: typically logarithmic in k, so the search space is small.
Edge cases: k=1, k=n, suffix length exceeding limit, minimum segment length.
Time complexity: O(log n) or O(log n * log n) if binary search with O(1) check.
Space complexity: O(1) extra space if only counting, O(k) if constructing output.
Alternative: direct formula if suffix length is constant, but here it's variable.

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