[理工] 離散 排容
可參考黃子嘉的第五版 上 5-54 5-55
選取SURREPTITIOUS
(a)exactly three pairs of consecutive identical letters
(b)at most three pairs of consecutive identical letters
C(x,y)表達組合 x取y
Sx指有x對連續
S3=C(5,3)* (10! / (2!)^2)
S4=C(5,4)* (9! / (2!))
S5=8!
解答a寫
E3=S3-C(4,1)*S4+C(5,2)*S5
解答b
N-L4=N-[S4-C(4,3)*S5]
想請教a 為什麼S4前要乘C(4,1) 跟S5 要乘C(5,2)
b 為什麼S5要乘C(4,3)
剛好三對不是用S3-S4就好了嗎
覺得S4跟S5完全包含於S3
謝謝
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