Flatten Deeply Nested Array
A medium-tier problem at 64% community acceptance, tagged with . Reported in interviews at Rivian and 4 others.
Flatten Deeply Nested Array is a medium-difficulty problem that shows up in assessments from PayPal, Rivian, Walmart Labs, and other companies. It's the kind of problem where the obvious loop fails, and you need to recognize the recursive or iterative pattern that actually works. Sixty-four percent acceptance rate sounds high, but that includes people who memorized it or happened to nail the trick on first try. If you hit this in a live online assessment and your first approach doesn't handle arbitrary nesting depth, StealthCoder surfaces a working solution invisible to the proctor so you can move on.
Companies that ask "Flatten Deeply Nested Array"
Flatten Deeply Nested Array is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe trap is thinking a single loop or a couple of nested loops will handle any depth. The actual trick is recognizing this is a traversal problem where you either use recursion to process each element and re-flatten its contents, or use a stack-based iterative approach that simulates the call stack. Common mistake: handling the first level correctly but not accounting for things nested three, four, or five levels deep. The algorithm itself is simple once you see it, but candidates who didn't practice with variable-depth inputs often get stuck mid-implementation. This is where StealthCoder's edge comes in. If you're confident in your recursion or stack logic, skip it. If you blank on structure or off-by-one errors start creeping in, an invisible reference solution keeps you from timing out on the problem.
You know the problem.
Make sure you actually pass it.
Flatten Deeply Nested Array recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Flatten Deeply Nested Array interview FAQ
Is this actually asked at PayPal and Rivian?+
Yes. The problem appears in reports from PayPal, Rivian, Walmart Labs, Otter.ai, and Yandex. It's more common at companies building systems that need to process hierarchical data. Expect it in backend or full-stack assessments, less likely in pure frontend screens.
What's the real trick nobody talks about?+
Most people try a for-loop first and realize it doesn't scale to arbitrary depth. The trick is recognizing you need recursion or an explicit stack. Once you frame it that way, the code writes itself. The problem isn't hard; it's about recognizing the pattern shift from iteration to traversal.
How much time should this take in a real OA?+
If you know the pattern, 5 to 10 minutes for a clean solution. If you're stuck between recursion and iteration, or debugging edge cases like empty arrays and single-element arrays, 15 to 20 minutes. That's why knowing it going in matters.
Do I need to memorize the solution?+
No. You need to recognize it's a traversal problem the moment you read it. Write pseudocode: check if element is a list, if yes recurse, if no add to result. Once you own that logic, implementation is mechanical. If you blank during the OA, StealthCoder is your safety net.
Does this connect to other topics I should know?+
Yes. This is fundamentally about recursion and depth-first traversal. Understanding it makes tree traversal, DFS, and backtracking problems feel natural. It's also good prep for any problem where you need to process nested structures like JSON or DOM trees.
Want the actual problem statement? View "Flatten Deeply Nested Array" on LeetCode →