Document Edit Events
Reported by candidates from ClickUp's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
This ClickUp OA, reported in October 2026, looks like a text editor problem but it's really a string simulation with strict validation. You get a list of INSERT and DELETE events, apply them in order, and reject anything out of range. No tricks hidden in the algorithm, just edge cases that punish sloppy bounds checks. If you blank on the validity rules during the live assessment, StealthCoder is the invisible safety net that reads the problem and hands you a working solution. But the logic here is short enough to own before you start.
The problem
A document starts as the empty string. Process each event in order and return the final document. ["INSERT", position, text] inserts text before the zero-based position. ["DELETE", position, length] removes length characters beginning at position. An event whose position or range is invalid for the current document is rejected and leaves the document unchanged. Function applyDocumentEdits(events: String[][]) → String Examples Example 1 events = [["INSERT","0","hello"],["INSERT","5"," world"],["DELETE","5","1"]] return = "helloworld" The second event adds a leading space before world, and the delete removes that space. Example 2 events = [["INSERT","0","abc"],["DELETE","4","1"],["INSERT","1","X"]] return = "aXbc" The out-of-range delete is rejected; the final insert succeeds. Constraints 0 <= events.length <= 20000. Inserted text and the final document together contain at most 200000 ASCII characters. Numeric fields are nonnegative decimal integers.
Reported by candidates. Source: FastPrep
Pattern and pitfall
The problem reduces to one question per event: is this edit valid for the current document length? For INSERT, position must be between 0 and len inclusive, since inserting at the end is allowed (Example 1 does exactly that). For DELETE, position must be less than len, and position plus length must be at most len. Anything else is skipped. The common pitfall is the off-by-one on INSERT, where people reject position equal to len. Another is forgetting that numeric fields arrive as strings, so parse them first. Also decide what a zero-length delete does, and handle it consistently with your range check. A plain string slice per event is O(n) each, so 20000 events against 200000 characters is workable in most languages. If you want safer performance, use a list of chunks or a rope-like structure. StealthCoder is your hedge in the live OA if the bounds logic slips under pressure.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Document Edit Events cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play.
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Document Edit Events FAQ
What's the trick in the ClickUp Document Edit Events problem?+
There isn't a clever algorithm. It's careful validation. INSERT allows position 0 through the current length inclusive. DELETE needs position plus length within the current length. Parse the string numbers to integers, check bounds, then slice. Most failures come from off-by-one errors, not from the approach.
How hard is this problem really?+
Easy on concepts, medium on carefulness. It's a simulation with two operations and a rejection rule. If you can write string slicing and bounds checks without bugs, you're done in minutes. The risk is missing an edge case like inserting at the very end or deleting past the end.
Will naive string concatenation be fast enough?+
Probably yes. With at most 20000 events and 200000 characters, rebuilding the string per event is roughly a few billion character copies in the worst case, which is borderline in slow languages. If you're nervous, store the document as a list of characters or chunks and edit in place.
What edge cases should I test before submitting?+
Test an empty events list, which returns an empty string. Test INSERT at position equal to length, INSERT past length, DELETE on an empty document, DELETE where position plus length overshoots, and DELETE with length 0. Also check Example 2, where a rejected delete must not change anything.
How do I prepare for this in 48 hours?+
Write the solution once from scratch and run both examples. Then add your own invalid cases: negative-looking inputs won't appear, but oversized positions will. Practice string slicing in your chosen language and parsing integers from strings. This pattern is simulation, so speed comes from clean bounds logic, not memorized tricks.