Find Missing Integers
Reported by candidates from IBM's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
IBM sent you a 'Find Missing Integers' problem in February 2024, and you've got limited time to lock in the pattern. This one rides the line between array manipulation and math, and candidates either see it immediately or blank hard under pressure. The trap is overthinking it. You need to know the two standard approaches (sorting/iteration vs. mathematical sum formula) and which one IBM's test environment actually wants. StealthCoder is your safety net if the logic slips during the live assessment.
Pattern and pitfall
The core trick here is recognizing that you're not searching for a missing element in a sorted sequence; you're finding one or more missing integers from a range. The math approach uses the formula for sum of integers 1 to n, then compares it to the actual sum of your input array to isolate the gap. The array approach sorts and iterates, catching breaks in sequence. The gotcha: whether the input is sorted, whether there's one missing integer or multiple, and what the bounds are. Most candidates waste time on edge cases instead of coding the straightforward path first. StealthCoder handles the syntax and bounds check instantly when you're live, so you can focus on communicating the logic to the interviewer.
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 Find Missing Integers 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
You've seen the question.
Make sure you actually pass IBM's OA.
IBM 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.
Find Missing Integers FAQ
Is this a hard problem?+
No. It's a medium at worst. The trick is spotting that it's fundamentally about arithmetic sum vs. array sum, or linear scan. Once you name the pattern, the code writes itself in under 10 minutes.
What's the most common wrong approach?+
Candidates try to use a hash set or binary search when they don't need to. Start simple: sum formula or iterate. Only optimize if you're told to handle a specific constraint or memory limit.
How do I prepare in 24 hours?+
Know the sum formula for integers 1 to n by heart. Practice one iteration-based solution on paper. Understand what 'missing' means in the problem statement. IBM values clarity over clever code.
Will there be a trick with duplicates or negatives?+
Possibly. Read the problem statement carefully for bounds and whether duplicates are allowed. If unsure, ask the interviewer during the OA. Don't assume it's a standard 1-to-n sequence.
Should I use sorting or the sum formula?+
Sum formula is O(n) time and O(1) space. Sorting is O(n log n) but sometimes more intuitive under pressure. Either works. Pick the one you can code without errors in two minutes.