Sum of Square Numbers
A medium-tier problem at 37% community acceptance, tagged with Math, Two Pointers, Binary Search. Reported in interviews at Two Sigma and 1 others.
Sum of Square Numbers lands on assessments from Two Sigma and LinkedIn, and candidates often blank on it because the obvious loop-through-all-squares approach feels slow. You're given a non-negative integer and asked whether it can be expressed as the sum of two perfect squares. It's not hard once you see the pattern, but the pattern isn't obvious from the problem statement alone. If this hits your live OA and you can't immediately picture the two-pointer technique that makes it efficient, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Sum of Square Numbers"
Sum of Square Numbers 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 trap is thinking you need to check every single perfect square and iterate through all possibilities, which balloons complexity. The real move is to recognize this as a two-pointer problem. Anchor pointers at the smallest and largest perfect squares that don't exceed the target, then walk them inward: if the sum is too small, move the left pointer up; if it's too large, move the right pointer down. The Math and Binary Search topics hint at this: you can binary search to find the perfect square root of a number, or use math to shrink the search space. Acceptance rate hovers around 36 percent, meaning roughly two-thirds of candidates either timeout or miss the trick. When you're live and the naive solution times out, StealthCoder hedges your prep gaps and delivers the two-pointer pattern instantly.
Pattern tags
You know the problem.
Make sure you actually pass it.
Sum of Square Numbers 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 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.
Sum of Square Numbers interview FAQ
Do I really need to check all perfect squares up to n?+
No. Use two pointers anchored at 0 and the integer square root of n. Walk them inward, comparing their sum to n. This cuts the time to O(sqrt n) instead of O(n). Most candidates who timeout use nested loops or check every square; the two-pointer approach dodges that.
Is this still asked at LinkedIn and Two Sigma?+
Yes. Both companies have confirmed asking it. Acceptance rate of 36 percent suggests it's not a gimme even among strong candidates. It's the kind of problem where the trick matters more than raw coding speed, so knowing the pattern pays off.
What's the relationship between Two Pointers and Binary Search here?+
Two pointers is the main approach: converge from opposite ends. Binary search plays a supporting role: you can use it to verify whether a number is a perfect square, or to find the square root boundary. Either framing works; two pointers is more direct.
What edge cases sink candidates on this one?+
Zero and one (both are sums of two squares trivially). Numbers that are already perfect squares. The largest valid pointer value when n is large. Most failures happen because candidates assume they need to iterate through all squares, not because of edge cases.
How long does this typically take in an interview?+
If you see the two-pointer pattern immediately, 10 to 15 minutes coding and testing. If you don't, you can spend 30+ minutes debugging a slow solution. That's why knowing the trick beforehand matters. StealthCoder is your insurance if the pattern doesn't click in the moment.
Want the actual problem statement? View "Sum of Square Numbers" on LeetCode →