Puzzleup 2019 (10) TWELVE BALLS - 拼圖

題目網址: http://www.puzzleup.com/2019/
http://www.puzzleup.com/2019/puzzle/?10
答題時限: 09月26日７ＰＭ－比賽結束
加分時限: 09月26日７ＰＭ－10月2日６：５９ＰＭ

答對可得基本分１００分。答案可上傳５次，每改１次答案從基本分扣２０分。　
比賽期間內可隨時上傳答案，加分時限內答對第ｎ天加（６－ｎ）分　 　　 　　
另依題目的難易有額外加分（如有８０％的人這題答錯，答對者加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?

有十二顆重量都不一樣的球。你要根據重量來排序這些球。有位朋友會幫忙排序。
每一步，你交給朋友4顆球，你朋友會依重量將這四顆球排序好，但是不告訴你每
顆球有多重。

問至少要經過幾次這樣的測量，才能保證這些球能按照重量排序。

--