Puzzleup 2015 (17) Ordered Codes - 拼圖

題目網址: http://www.puzzleup.com/2015/
http://www.puzzleup.com/2015/puzzle/?17
答題時限: 11月19日７ＰＭ－比賽結束（約12月16日）
加分時限: 11月19日７ＰＭ－11月25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）　　

◆ORDERED CODES

How many 25-letter codes formed by using the letters A, B, C, D and E have
their letters in alphabetical order?

有多少長 25 字母，使用 A,B,C,D,E 五種字母的編碼，
具有編碼中的字母是以字母順序排列的性質？

If the problem was asked for 4-letter codes with the letters A, B, and C,
the answer would be 15:

若題目改問長 4 字母，使用 A,B,C 三種字母的話，答案為 15：

AAAA, AAAB, AAAC, AABB, AABC,
AACC, ABBB, ABBC, ABCC, ACCC,
BBBB, BBBC, BBCC, BCCC, CCCC.

--
'Oh, Harry, don't you see?' Hermione breathed. 'If she could have done
one thing to make absolutely sure that every single person in this school
will read your interview, it was banning it!'
---'Harry Potter and the order of the phoenix', P513

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