Coin Weighing Puzzle Quant Interview Guide
Coin weighing puzzle quant interview guide for balance-scale outcomes, information counting, case splitting, examples, and common mistakes.
Candidates practicing information, branching, and search logic.
Each weighing gives limited information
A balance-scale weighing can tilt left, tilt right, or balance. Counting these possible outcomes helps estimate whether a proposed strategy can distinguish all cases.
Design branches deliberately
A good coin-weighing strategy splits remaining possibilities into groups that can be separated by the remaining weighings. Uneven branches waste information.
Concrete example
If one coin may be heavier among nine coins, a first weighing of three against three can split the possibilities into left-heavy, right-heavy, and unweighed groups.
Track heavy versus light variants
Some variants say the odd coin may be heavier or lighter. That doubles the hypothesis space and changes how much information each weighing must extract.
Common mistakes
Candidates often memorize one classic solution and miss variant details. State the number of coins, whether odd means heavy or light, and allowed weighings.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.