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我正在尝试编写当 X 是系数、Y 是指数并且 R 应该返回答案时获得 3 个参数的代码。

到目前为止,我的代码是 -

exp(X,0,R):- R is X*X.
exp(X,Y,R):- Y1 is Y-1, exp(X,Y1,R).

我知道这行不通。

但我无法弄清楚。

4

1 回答 1

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看一下这个:

3 ?- X is 5 // 2, Y is 5 rem 2.
X = 2,
Y = 1.
4 ?- 0 is 5 rem 2.
false.

所以,

R being X^Y is the same as
   R being .....
         when Y is 0, OR
   R being .....
         when Y is 1, OR
   R being R2*R2 and R2 being X^Y2
         when Y is even, Y2 is Y // 2, OR
   R being ..... and R2 being X^Y2
         when Y is odd, Y2 is (Y-1) // 2.

或者,在 Prolog 中,

is_power(R,X,Y):- Y is 0, R is ... .
is_power(R,X,Y):- Y is 1, R is ... .
is_power(R,X,Y):- Y > 1, ... , is_power(R2,X,Y2), R is ... 
...

要编写您要求的代码,您只需减 1 而不是减半(当然,相应地更改其余代码)。

于 2015-02-05T11:37:06.150 回答