題目網址: http://www.puzzleup.com/2014/
http://www.puzzleup.com/2014/puzzle/?251
答題時限: 10月２日７ＰＭ－比賽結束（約12月17日）
加分時限: 10月２日７ＰＭ－10月８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）　　
◆Five-Letter Code
You will produce five-letter codes using the letters A, B, C, D, and E.
You are not allowed to produce a code that can be constructed by
interchanging any two adjacent letters of an existing code.
What is the maximum number of different codes that can be produced according
to this rule?
If the problem was asked for three-letter codes using the letters A, B, and C,
then the answer would be 18.
AAA, AAB, AAC, ABB, ABC, ACC,
BAA, BBA, BBB, BBC, BCA, BCC,
CAA, CAB, CBB, CCA, CCB, CCC.
你要使用 A B C D E 五個字母組成長度為五的編碼，
但你不能使用已有編碼中交換相鄰兩個字母所形成的編碼。
試問最多可以組成多少個編碼？
若題目改問 A B C 三個字母組成長度三的編碼, 則答案為 18：
AAA, AAB, AAC, ABB, ABC, ACC,
BAA, BBA, BBB, BBC, BCA, BCC,
CAA, CAB, CBB, CCA, CCB, CCC.