Chain Merge
Reported by candidates from Rubrik's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Rubrik's September OA included a problem called Chain Merge, and it's testing your ability to combine or flatten data structures efficiently. You're being asked to handle multiple arrays or sequences and produce a single coherent output. This is a classic array manipulation pattern that trips up candidates who overthink the merge order or don't catch the optimal approach. If you blank during the live OA, StealthCoder will read the problem on screen and show you the pattern in real time, letting you focus on clean code.
Pattern and pitfall
Chain Merge is fundamentally about merging or concatenating multiple arrays into one result, often with constraints on order, deduplication, or cost. The trick is recognizing whether you need a simple linear merge, a priority-based merge, or a greedy selection across chains. Common pitfalls: assuming you must process chains sequentially when you can actually pick from any chain at each step, or missing that the 'cost' of merging is tied to the order you select elements. Most solutions fall into greedy or simulation buckets. During the live OA, if you're unsure whether to BFS or greedily pick the minimum, StealthCoder will show you which branch works. The key insight is usually that you can iterate through and pick the cheapest or best next element, not that you're forced into one fixed order.
If you see this problem in your OA tomorrow, the play is to recognize the pattern in 30 seconds. StealthCoder buys you that recognition.
You can drill Chain Merge 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 by an Amazon engineer who passed his OA cold and still thinks the filter is broken.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as merge k sorted lists. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass Rubrik's OA.
Rubrik reuses patterns across OAs. Built by an Amazon engineer who passed his OA cold and still thinks the filter is broken. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Chain Merge FAQ
Is this a hard array problem or a medium?+
It reads medium. You're not doing dynamic programming or advanced data structures. It's about understanding the merge strategy and implementing it cleanly. The 'hard' part is recognizing whether you need a heap, greedy selection, or simple simulation.
Do I need to sort the input arrays?+
Not necessarily. Many candidates default to sorting, but the problem often gives you the order for a reason. Read carefully. If the problem says chains have an inherent order, respect it. Otherwise, sorting may be a red herring.
What's the most common mistake on this one?+
Assuming you must merge chains left to right or in a fixed sequence. The real trick is usually that you can pick from any chain at each step, and you want to minimize cost or maximize some metric. Think greedy or use a min-heap to always pick the best next element.
Will my brute force solution pass?+
Depends on the constraints. If you're merging N chains of M elements, a naive nested loop is O(N*M^2) at worst. Rubrik usually sets limits where that times out. A greedy or heap-based solution is safer and still straightforward to code.
How do I prep for this in 48 hours?+
Study merge operations in arrays and lists. Understand when to use a heap for 'always pick the best.' Scan LeetCode 'merge k lists' and greedy merge problems. The concept is nearly always the same: pick smartly, don't brute force, and use a data structure to avoid rescanning.