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Hard · Brainteasers · Quant Trader interview question · binary-search, ternary-search, decision-tree
You are auditing a ledger of 12 identical-looking cryptocurrency hardware wallets ("coins"). One is a counterfeit and has a slightly different weight (you don't know if it is heavier or lighter). You have a balance scale that tells you if the left side is heavier, lighter, or equal to the right side. What is the minimum number of weighings required to guarantee you find the counterfeit and determine if it is heavier or lighter?