Valid Perfect Square
A easy-tier problem at 44% community acceptance, tagged with Math, Binary Search. Reported in interviews at LinkedIn and 2 others.
Valid Perfect Square is an easy-tier problem that shows up in live assessments at LinkedIn, SAP, and TCS. The 44% acceptance rate tells you something: candidates either nail it instantly or burn time on the obvious approach. The problem asks you to determine if a given positive integer is a perfect square. Sounds trivial. It isn't, because the naive loop gets flagged as inefficient, and you need to know which algorithmic tool fits. If this problem hits your live OA and you blank on the pattern, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Valid Perfect Square"
Valid Perfect Square 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 trick is recognizing that this is a search problem, not a math problem. Binary search over the range 1 to n finds the square root in logarithmic time, which crushes a brute-force linear scan. Most candidates default to the loop and get rejected for efficiency. You could also use Newton's method or the mathematical property that perfect squares have specific divisibility patterns, but binary search is the clean, interview-safe win. The edge case to watch: overflow on mid*mid in some languages, and the boundary conditions on left and right. StealthCoder surfaces the binary search frame immediately if you're stuck on optimization, so you don't waste five minutes defending a slow solution.
Pattern tags
You know the problem.
Make sure you actually pass it.
Valid Perfect Square 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. 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.
Valid Perfect Square interview FAQ
Is this actually asked at FAANG level, or just tier-2 companies?+
LinkedIn asks it, which is a major feather. The 44% acceptance rate suggests it's harder than the difficulty tag implies. Companies use it as a filter for binary search fluency, not a warmup. If you see it live, treat it seriously.
What's the trick if the obvious loop times out?+
Binary search from 1 to n. Check if mid*mid equals the target. If mid*mid is less, move left boundary up. If greater, move right boundary down. O(log n) beats O(n) instantly. That's the entire pattern.
Does the Math topic mean I need calculus or number theory?+
No. The Math tag just means the problem is number-oriented. You don't need advanced math. Binary Search is the core topic. If you're comfortable with BS, you're covered.
Are there gotchas with integer overflow or edge cases?+
Watch mid*mid overflow in languages like C++ or Java. Use mid*mid == num carefully, or cast to long. Edge cases: n=1 (is 1 a perfect square? yes), n=2 (is 2? no). Boundary logic on left and right pointers matters.
Should I memorize all perfect squares, or learn the algorithm?+
Learn the algorithm. Memorizing is brittle and fails on large numbers. Binary search generalizes to root-finding across problem variants. That's why LinkedIn and SAP ask it: they want to see if you think algorithmically, not if you cramped.
Want the actual problem statement? View "Valid Perfect Square" on LeetCode →