题目网址: http://www.puzzleup.com/2019/
http://www.puzzleup.com/2019/puzzle/?10
答题时限: 09月26日７ＰＭ－比赛结束
加分时限: 09月26日７ＰＭ－10月2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）
◆TWELVE BALLS
There are 12 balls with all different weights. You want to sort these
balls by weight. You have a friend who will help you with the ordering
process. In each step, you give any 4 balls to your friend and your
friend returns their exact weight order without telling their actual
weight.
What is the minimum number of measurements do you need in order to
guarantee to sort the balls correctly by weight?
有十二颗重量都不一样的球。你要根据重量来排序这些球。有位朋友会帮忙排序。
每一步，你交给朋友4颗球，你朋友会依重量将这四颗球排序好，但是不告诉你每
颗球有多重。
问至少要经过几次这样的测量，才能保证这些球能按照重量排序。