Append Deranged CSV Rows
Reported by candidates from Clio's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Clio's OA from January 2024 looks like a CSV puzzle, but it's a left rotation problem wearing a costume. Read the first paragraph and it sounds like you need to generate derangements. You don't. The statement hands you the exact construction: rotate each row one position left, then append those rows after the originals. If you've got an invite and 48 hours, this one is a warmup, not a wall. StealthCoder sits invisibly on your screen as a safety net if you blank on the details mid-assessment, but you probably won't need it here.
The problem
Given parsed CSV rows, append one derangement of every original row. In a derangement, every value moves to a different column from its position in that original row. For deterministic judging, construct each deranged row by rotating its values one position to the left. Return all original rows in order, followed by their rotated rows in the same order. Function appendDerangedRows(rows: String[][]) → String[][] Examples Example 1 rows = [["a","b","c"],["1","2"]] return = [["a","b","c"],["1","2"],["b","c","a"],["2","1"]] Each appended row is a left rotation, so no value stays in its original column. Constraints 1 <= rows.length <= 1000. 2 <= rows[i].length <= 100. Values within each row are distinct strings.
Reported by candidates. Source: FastPrep
Pattern and pitfall
What it really reduces to: copy the input, then for each row build a new row where element i becomes element (i+1) mod n. That's it. Output is the originals in order, then the rotated rows in the same order. The trick is ignoring the word derangement, because the rotation is dictated and the constraint of at least 2 values per row, all distinct, guarantees nothing stays in its column. The common pitfalls are mutating the input rows while rotating, so build new arrays, and putting rotated rows right after each original instead of after all originals. Example 1 shows the order clearly. Complexity is O(total cells) time and space, which is trivial at 1000 rows by 100 columns. If you freeze on the ordering or an off-by-one on the rotation, StealthCoder is the hedge on the live OA, but a slice and concatenate gets you there in a few lines.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Append Deranged CSV Rows 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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Append Deranged CSV Rows FAQ
How hard is the Clio Append Deranged CSV Rows question really?+
Easy. The name suggests combinatorics, but the statement fixes the construction as a one-step left rotation. It's array manipulation with a clear example. Most of the risk is misreading the output order or accidentally modifying the input rows.
What's the trick to this problem?+
Ignore the derangement theory. Take each row, move the first element to the end, and collect the results. Return the original rows first, then all rotated rows in the same order. Distinct values and length of at least 2 make the derangement property automatic.
What order should the output rows be in?+
All original rows first, in input order, then all rotated rows in the same input order. Example 1 shows it: the two originals, then the rotated version of row one, then the rotated version of row two. Don't interleave them.
What's the time complexity I should state?+
O(R * C) time and space, where R is the number of rows and C is the row length. You touch every cell once to copy it and once to rotate it. With at most 1000 rows of 100 values, performance isn't a concern.
How do I prepare for this in 48 hours?+
Practice array slicing and index arithmetic in your chosen language. Write a rotate-left helper, test it on rows of length 2 and 3, and confirm you build new arrays instead of mutating the input. Then spend the remaining time on harder array and hash-table problems.