使用序言替换两个列表之间的元素 [英] replacing elements between two lists using prolog

问题描述

我的任务是制作myReplace(E1,L1,E2,L2)，以使L1中最早出现的E1替换为E2，并在L2中返回.我已经写了下面描述的代码，它可以正常工作.

My task is to make myReplace(E1,L1,E2,L2) such that the very first occurrence of E1 in L1 gets replaced by E2 and is returned in L2. I have written the below described code and it is working properly.

myReplace(E1,[],E2,[]).
myReplace(E1,[E1|Xs],E2,[E2|Ys]):-
  myReplace(E1,Xs,E1,Ys).
myReplace(E1,[H|Hs],E2,[H|Ts]):-
  E1 \= H,
  myReplace(E1,Hs,E2,Ts).

但是，例如myReplace(2,[1,2,3,2,1],5,X)应该给出X = [1,5,3,2,1]和X = [1,2,3,5,1].但是我的代码只给出了一个解决方案，即X = [1,5,3,2,1].

However, For example myReplace(2,[1,2,3,2,1],5,X) should give X = [1,5,3,2,1] and X = [1,2,3,5,1]. But my code is only giving one solution which is X = [1,5,3,2,1].

类似地，当myReplace(2,X,5,[1,5,3,5,1])应该仅回溯解决方案X = [1,2,3,5,1]和X = [1,5,3,2,1]时，但是我的解决方案为我提供了另一个解决方案，如X = [1,5,3,5,1].

Similarly, when myReplace(2,X,5,[1,5,3,5,1]) should backtrack over the solutions X = [1,2,3,5,1] and X = [1,5,3,2,1] only, but my solution gives me one more solution as X = [1,5,3,5,1].

您能帮我解决这个问题吗?

Could you please help me resolve this.

谢谢:)

推荐答案

关于

myReplace(E1,[E1|Xs],E2,[E2|Xs]).

myReplace(E1,[H|Hs],E2,[H|Ts]):-
  myReplace(E1,Hs,E2,Ts).

?

如果我没记错的话，这将强制进行一次(并且只有一次)替代.

If I'm not wrong, this impose one (and only one) replacement.

记入您必须删除的内容

myReplace(E1,[],E2,[]).

否则，您会得到L1 = L2(无替代品)作为解决方案.

otherwise you get L1 = L2 (no replacement) as a solution.

并观察到，正如Lurker所指出的，这不是"L1中E1的第一次出现被替换".

And observe that, as pointed by Lurker, this isn't "the very first occurrence of E1 in L1 gets replaced".

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