[英]Prolog Binary Addition Issue?
I have this piece of homework that I have to write in Prolog.The requirement is to write a piece of code that does binary addition such as: 我有这篇文章我必须在Prolog中编写。要求是编写一段代码来执行二进制加法,例如:
?- add([1,0,1],[1,1],X).
X = [0,0,0,1]
And so, this is the code that I came up with: 所以,这是我提出的代码:
add([],[], _).
add([],Y, Z) :- append([], Y, Z).
add(X,[], Z) :- append(X,[],Z).
add([HX|TX],[HY|TY], Z) :-
HX = 1,
HY = 1,
add(TX,TY, Z1),
add([1],Z1, Z2),
append([0],Z2,Z),!.
add([HX|TX],[HY,TY], Z) :-
HX = 0,
HY = 1,
add(TX,TY,Z1),
append([1],Z1, Z),!.
add([HX|TX],[HY|TY], Z) :-
HX = 1,
HY = 0,
add(TX,TY,Z1),
append([1],Z1, Z),!.
add([HX|TX],[HY,TY], Z) :-
HX = 0,
HY = 0,
add(TX,TY,Z1),
append([0],Z1, Z),!.
It seems to do what I needed, however, there are strange issues with it that I can not understand, so if someone could guide me to what I have done wrong, I would be glad. 它似乎做了我需要的东西,然而,它有一些我无法理解的奇怪问题,所以如果有人可以指导我做错了什么,我会很高兴的。
Results: 结果:
?- add([1,1,1,1], [1,1],Z).
Z = [0, 1, 0, 0, 1]. % this is correct
?- add([1], [1],Z).
Z = [0, 1]. % this is correct
?- add([1,1,0,1], [1,1],Z).
Z = [0, 1, 1, 1]. % this is correct
?- add([1],[0],Y).
Y = [1|_G7100]. % there is an error here, but its not the big issue.
?- add([1,0,1], [1,1],Z).
false. % no results are returned.
104 ?- add([0], [1],Z).
false. % no results returned either
Problem: Whenever there seems to be a 0 in the first binary list, under some conditions(still trying to figure them out), no results seems to be returned.but I can't seem to locate my error.Would be glad if someone can tell me what I did wrong. 问题:每当第一个二进制列表中似乎有一个0,在某些条件下(仍然试图弄清楚它们),似乎没有返回结果。但我似乎无法找到我的错误。如果有人会很高兴可以告诉我我做错了什么。
There are 3 mistakes: 有3个错误:
add([],[],[]).
规则#1:应该add([],[],[]).
instead of add([],[], _).
而不是add([],[], _).
. 。 This fails for equal-length lists. 这对于等长列表来说是失败的。 add([HX|TX],[HY|TY], Z)
instead of add([HX|TX],[HY,TY], Z)
. 规则#5和#7:应该add([HX|TX],[HY|TY], Z)
而不是add([HX|TX],[HY,TY], Z)
。 This fails when the second list ( Y
) contains less than two elements. 当第二个列表( Y
)包含少于两个元素时,这会失败。 Fix these and your code should run well: see here . 修复这些并且您的代码运行良好:请参阅此处 。
I see you use 7 different rules, since you put the binary arithmetic inside the rules. 我看到你使用7种不同的规则,因为你把二进制算术放在规则中。 You can do with 6 different rules plus a start rule as follows: 您可以使用6个不同的规则和一个启动规则,如下所示:
add2(AL, BL, CL) :-
add2(AL, BL, 0, CL).
add2([A | AL], [B | BL], Carry, [C | CL]) :-
X is (A + B + Carry),
C is X rem 2,
NewCarry is X // 2,
add2(AL, BL, NewCarry, CL).
add2([], BL, 0, BL) :- !.
add2(AL, [], 0, AL) :- !.
add2([], [B | BL], Carry, [C | CL]) :-
X is B + Carry,
NewCarry is X // 2,
C is X rem 2,
add2([], BL, NewCarry, CL).
add2([A | AL], [], Carry, [C | CL]) :-
X is A + Carry,
NewCarry is X // 2,
C is X rem 2,
add2([], AL, NewCarry, CL).
add2([], [], Carry, [Carry]).
Here are some example runs: 以下是一些示例运行:
?- add2([1,1,1,1], [1,1],Z).
Z = [0,1,0,0,1]
?- add2([1], [1],Z).
Z = [0,1]
?- add2([1,1,0,1], [1,1],Z).
Z = [0,1,1,1]
?- add2([1],[0],Y).
Y = [1]
?- add2([1,0,1], [1,1],Z).
Z = [0,0,0,1]
?- add2([0], [1],Z).
Z = [1]
Main advantage of the above solution, less invocations of add2/4 and you could replace the //2 and rem 2, and do addition in some other number system as well. 上述解决方案的主要优点是,add2 / 4的调用较少,你可以替换// 2和rem 2,并在其他数字系统中添加。
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