Missing Element in Sorted Array
A medium-tier problem at 59% community acceptance, tagged with Array, Binary Search. Reported in interviews at Arista Networks and 0 others.
You're looking at a problem that sounds simple on the surface: find a missing element in a sorted array. Arista Networks asks this one. At first it feels like a trivial loop, but the actual constraint is that you need to do it efficiently. The obvious O(n) approach works, but if you waste time on it during the OA, you're leaving points on the table. This is where the binary search pattern kicks in and separates candidates who've actually studied from those who just brute force. If this problem hits your live assessment and you blank on the binary search angle, StealthCoder runs invisibly and surfaces the optimal solution in seconds.
Companies that ask "Missing Element in Sorted Array"
Missing Element in Sorted 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick here is recognizing that you can't just check if each element is missing because the array is sorted and you have a known range. The real pattern: use binary search to pinpoint where the expected value diverges from the actual value. In a sorted array without gaps, element at index i should equal start_value plus i. When it doesn't, you've found your boundary. Most candidates default to iterating through and comparing differences, which works but tanks on large inputs. The gap between O(n) and O(log n) is the gap between passing and impressing. This is the kind of problem that looks deceptively straightforward until you realize the interviewer is testing whether you reflexively think in terms of binary search on sorted data. If you freeze during the OA, StealthCoder gives you the working code so you move on without tanking your score.
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Missing Element in Sorted 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 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.
Missing Element in Sorted Array interview FAQ
Is this problem really asked at Arista Networks?+
Yes. Arista reports this one. It's not a trick question in hiring strategy, but it does test whether you can optimize beyond brute force. That's a signal they care about efficiency in your thinking, not just correctness.
What's the actual trick I'm supposed to see?+
Use binary search to find where the sorted array diverges from expected values. Element at index i should be start_value plus i if there's no gap. When the offset breaks, you've found your missing number. O(log n) beats the loop.
How does this relate to array and binary search topics?+
It's the intersection. Arrays are the surface, but the problem only has an elegant solution if you think in binary search terms. It teaches you to apply binary search to problems that don't scream 'binary search' at first glance.
Will iterating through and checking differences fail me?+
Not necessarily. With 58% acceptance, brute force passes many test cases. But it's suboptimal and signals you're not thinking algorithmically. On a live OA, the binary search version is the difference between 'okay' and 'solid engineer' feedback.
How hard is this really for a medium problem?+
The acceptance rate of 58% suggests the gap between obvious and optimal is significant. The concept is straightforward, but the optimization requires you to have internalized binary search as a reflex on sorted data problems.
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