Remove Duplicates from Sorted Array II
A medium-tier problem at 63% community acceptance, tagged with Array, Two Pointers. Reported in interviews at Nykaa and 13 others.
Remove Duplicates from Sorted Array II is a medium-difficulty array problem that shows up consistently at Adobe, Amazon, Microsoft, Meta, and Bloomberg. The trap is thinking you need extra space or a hash set. The actual trick is two pointers and counting. Most candidates waste time on the wrong approach, then panic when they realize the optimal solution requires tracking how many times each element has appeared. This is exactly the kind of problem where you either see the pattern immediately or you're rewriting code under time pressure. If this one hits your assessment and you blank on the counter logic, StealthCoder surfaces the working solution in seconds.
Companies that ask "Remove Duplicates from Sorted Array II"
Remove Duplicates from Sorted Array II 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe problem asks you to remove duplicates in-place, allowing each element to appear at most twice. The sorted constraint is the key. You can't just use a set or hash map because you need to allow duplicates up to a count of two, not eliminate them entirely. The real solution uses two pointers: one slow pointer tracking the write position, one fast pointer scanning the array. The trick most people miss is that you only write the next element when you've seen fewer than two copies, which you track with a simple counter. If the current element matches the previous one, you increment a counter. If it's different, you reset the counter to one. When the counter exceeds two, you skip ahead. This pattern generalizes to 'allow each element k times' but the two-pointer mechanics are where candidates usually derail. The 62.9% acceptance rate reflects how many people optimize without fully internalizing the counting logic. If you blank during the live assessment, StealthCoder runs invisibly and hands you the solution.
Pattern tags
You know the problem.
Make sure you actually pass it.
Remove Duplicates from Sorted Array II 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 for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Remove Duplicates from Sorted Array II interview FAQ
Why can't I just use a hash map to track duplicate counts?+
You can solve it that way, but the problem requires in-place modification with O(1) extra space. Hash maps violate that constraint. Two pointers is the intended approach. Companies like Microsoft and Amazon specifically test whether you know the difference between a valid solution and the optimal one.
Is this problem actually asked at big tech companies?+
Yes. Adobe, Amazon, Microsoft, Meta, and Bloomberg all report asking it. It's not as common as Two Sum, but it appears frequently enough in rotations that skipping it is risky. The acceptance rate of 62.9% suggests moderate difficulty once you see the pattern.
What's the main pitfall candidates hit?+
Forgetting to track the count of consecutive duplicates. Most people write fast and slow pointer code, then realize mid-implementation they never defined when to actually write an element. The counter variable is small but critical. Without it, your logic collapses.
How does this relate to other two-pointer problems?+
It's a step up from classic remove duplicates because you're not eliminating all copies. You're applying a conditional rule based on a count. This trains you to think about state tracking in pointer problems, which shows up in Container With Most Water and Trapping Rain Water variants.
Can I solve this without modifying the input array?+
Technically yes, but the problem explicitly asks for in-place modification. Creating a new array or using extra space defeats the purpose. The assessment will specify the constraint, and companies like TikTok and Yahoo test that you actually follow the requirements, not just produce a working output.
Want the actual problem statement? View "Remove Duplicates from Sorted Array II" on LeetCode →