Chalkboard XOR Game
A hard-tier problem at 63% community acceptance, tagged with Array, Math, Bit Manipulation. Reported in interviews at HashedIn and 0 others.
Chalkboard XOR Game is a deceptive problem that trips up candidates who jump straight to simulation. You see a game, think game theory, and immediately try to model player states. But the actual solution hinges on a single mathematical insight about XOR that makes the entire game tree collapse into a one-line answer. It's asked by HashedIn and sits at 63% acceptance, which tells you most people who pass it figured out the trick. Most who fail it didn't. This is exactly the kind of problem where StealthCoder pays for itself: if you hit it live and your brain goes blank on the pattern, a working solution surfaces invisibly in seconds.
Companies that ask "Chalkboard XOR Game"
Chalkboard XOR Game 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 simulate both players playing optimally. You don't. The key is recognizing that XOR has a fixed mathematical property: the XOR of all numbers on the board never changes, regardless of which numbers players erase. Once you see that, you realize the game's outcome is determined before the first move. The trick involves checking whether the initial XOR value meets a specific condition, and suddenly a complex game-theory problem becomes a bit manipulation one-liner. Most candidates burn 20 minutes trying to build a recursive game tree before they backtrack. When the brainteaser clicks, it's fast. When it doesn't, you're stuck. StealthCoder handles the moment you realize you've been overthinking it.
Pattern tags
You know the problem.
Make sure you actually pass it.
Chalkboard XOR Game recycles across companies for a reason. It's hard-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.
Chalkboard XOR Game interview FAQ
Is this really a hard problem or does it feel harder than it is?+
It's genuinely hard because the solution method doesn't match the problem's appearance. Game theory problems usually require DP or recursion. This one needs XOR insight. That mismatch between presentation and approach is why 63% is the acceptance rate, not higher. The math is simple once you see it.
What's the core trick I need to know?+
The XOR of all board values is invariant. No matter what players erase, the XOR result at game end is fixed from the start. This means you're not actually simulating a game; you're checking one mathematical condition. That's the pattern that unlocks it.
How does bit manipulation connect to the game outcome?+
Bit manipulation isn't the hard part; it's the language. XOR is a bitwise operation, but you're using it to encode game state as a single number. The game's winner is determined by whether that number meets a threshold. Bit manipulation is just the tool, game theory is the trap.
Should I simulate or should I look for a pattern?+
Pattern first. If your solution involves recursion or DP to explore game states, you're probably on the wrong track. The correct insight is mathematical, not algorithmic. Simulation feels natural; the pattern feels strange until it clicks.
How does HashedIn typically ask this in a real OA?+
The problem statement will describe two players taking turns erasing numbers. It looks like a game you have to model. The expectation is that you spot the invariant property early and pivot to the math. Candidates who do usually solve it in 10 minutes. Those who don't can spend the whole hour stuck.
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