離散 函數跟基本關係
看到兩題題目分別如下
X={x1,x2......xm}, Y={y1,y2......yn}
with lXl=m and lYl=n
(a)How many relations are there fromX toY?
(b)How many functions f: X -> Y satisfy f(x1)=f(xm)=yn
a的答案是2^mn
b的答案是n^m-2
我想請問(a)為什麼不為n^m呢？
觀念有點不清QQ
感謝大家~
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