最重的硬币
Heaviest Coin
题目详情
给你 9 个硬币和一个老式天平。所有硬币的重量都相同，除了一枚比其他硬币重。在只能使用秤两次的情况下，如何确定哪枚硬币最重？
You are given 9 coins and one old-fashioned balance scale. All coins weigh the same, except one which is heavier than the rest. How would you determine which coin is the heaviest while only being able to use the scale twice?
解析
首先将每个硬币标记为 1 到 9。将硬币 1、2 和 3 放在左侧天平上，将硬币 4、5 和 6 放在右侧天平上。如果天平平衡，我们知道最重的硬币一定是 7、8 或 9。如果天平向左倾斜，我们知道最重的硬币一定是 1、2 或 3，如果天平向右倾斜，我们知道最重的硬币一定是 4、5 或 6。
现在我们已经将硬币范围缩小到三种选择，我们将再次重复该过程。让我们标记剩下的三个硬币：1、2 和 3。将硬币 1 放在左侧刻度上，将硬币 2 放在右侧刻度上。如果天平平衡，我们知道最重的硬币是硬币 3，如果天平向左倾斜，我们知道最重的硬币是硬币 1，如果天平向右倾斜，我们知道最重的硬币是硬币 2。
Original Explanation
First label each coin from 1 to 9. Place coins 1, 2, and 3 on the left balance and coins 4, 5, and 6 on the right balance. If the scale is balanced, we know that the heaviest coin must be coin 7, 8, or 9. If the scale tilts left, we know that the heaviest coin must be 1, 2, or 3 and if the scale tilts right we know that the heaviest coin must be 4, 5 or 6.
Now that we have narrowed down the coins to three choices we will repeat the procedure once again. Lets label the three remaining coins, 1, 2, and 3. Place coin 1 on the left scale and coin 2 on the right scale. If the scales are balanced, we know that the heaviest coin is coin 3, if the scale tilts left we know the heaviest coin is coin 1, and if the scale tilts right we know that the heaviest coin is coin 2.