题目网址: http://www.puzzleup.com/2018/
http://www.puzzleup.com/2018/puzzle/?10
答题时限: １０月4日７ＰＭ－比赛结束（约12月12日）
加分时限: １０月4日７ＰＭ－１０月10日６：５９ＰＭ
答对可得基本分１００分。答案可上传５次，每改１次答案从基本分扣２０分。
比赛期间内可随时上传答案，加分时限内答对第ｎ天加（６－ｎ）分
另依题目的难易有额外加分（如有８０％的人这题答错，答对者加８０分）
◆SCALE
There are X balls that look identical. All balls except one has the same
weight. The different ball is either lighter or heavier than the others.
You have a balance scale with two plates and you can only use it to compare
the weights of the balls. With each use you can put any number of balls in
each plate and as a result find out which side is heavier or if the two
sides have the same weight.
You can guarantee finding the different ball and whether it is lighter
or heavier by using the scale at most 4 times. What is the maximum possible
X satisfying this condition?
有X颗外观一样的球。每颗球具有相同的重量，除了其中一颗。该颗球或许比其它
球重，或是较轻。
你有一个天秤，带两个底座，只可用来比较球的重量。每次使用时，你在各底座上
放置任意数量的球，并可得到哪边较重或是一样重的结果。
在至多使用天秤四次的情形下，你能保证可以找出重量不一样的球，且能知道该颗
球是较轻或较重的。问能满足上述前提之最大可能X值？