Missing Number
A easy-tier problem at 70% community acceptance, tagged with Array, Hash Table, Math. Reported in interviews at Warnermedia and 15 others.
Missing Number is an easy problem that shows up at Google, Tesla, Nvidia, and a dozen other serious companies. You're given an array containing n distinct numbers from 0 to n. One is missing. Find it. The acceptance rate is 70%, which means 30% of candidates either solve it slowly, pick the wrong approach, or blank under pressure. The obvious answers (hash table, sorting) work but miss the elegance that interviewers actually want. If you hit this live and freeze on the clever tricks, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Missing Number"
Missing Number 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. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderThe naive approaches all work: build a set, check which number is absent, or sort and scan. But the problem is really a test of whether you can see the mathematical patterns. The sum trick is the most common: total expected sum minus actual sum equals the missing number. XOR is faster and more elegant because a XOR a equals 0, so XORing all indices with all array values cancels everything except the missing one. Bit manipulation and math are in the topic list for a reason. Interviewers want to see if you recognize the structure, not just brute force. When you're on the clock and the obvious solution feels too simple, that's when doubt creeps in and you second-guess yourself. StealthCoder is the hedge for that moment, handling any approach you missed so you can move forward.
Pattern tags
You know the problem.
Make sure you actually pass it.
Missing Number recycles across companies for a reason. It's easy-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. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Missing Number interview FAQ
How does the XOR solution work for Missing Number?+
XOR has the property that a XOR a equals 0 and a XOR 0 equals a. So if you XOR all indices 0 to n with all array values, the duplicates cancel to 0, leaving only the missing number. It's faster than the sum trick and avoids integer overflow risk.
Is Missing Number still asked at Google and Tesla?+
Yes. Google and Tesla are both in the top companies list. It's a classic easy that interviewers use to see how you think about trade-offs between approaches, not just whether you can code a solution.
What's the main pitfall candidates hit on this problem?+
Picking a single approach and coding it without considering the alternatives. Hash table and sum both work, but they don't show pattern recognition. The question is really testing whether you see the mathematical structure underneath.
Can you solve Missing Number with sorting?+
Yes, sort the array and scan for the gap. It works but is O(n log n) when O(n) solutions exist. In an interview, mentioning this approach shows you know the full landscape, but not pursuing the faster route signals you missed the pattern.
Why is Missing Number marked easy if companies like Google ask it?+
The core logic is straightforward, but interviewers care about your reasoning: which approach you pick, why you pick it, and whether you recognize the elegant solutions. Easy difficulty means the problem is solvable. Hard interviews mean the conversation around it.
Want the actual problem statement? View "Missing Number" on LeetCode →