Im learning Prolog and im trying to write a clause that check if one list (L1) is de result of duplicate other List(L2) N times,and return N as de result of checking how many times L2 is duplicated in L1. But I dont know how to compare the elements of two lists of different size and count how many times L2 is duplicated. Can you help me?.
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Forget about Prolog and think: how would you do it by hand? – salva May 18 '21 at 07:33
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Looks like this could be your answer: https://stackoverflow.com/questions/67568087/method-that-counts-the-number-of-occurs-in-one-list-in-prolog – David Tonhofer May 18 '21 at 07:34
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One solution that comes to mind is using append/3. Since
append/3 is able to consume the beginning prefix of a list:
?- append([1,2],X,[1,2,3,5]).
X = [3, 5].
So a quite straight forwards solution does the following,
assuming the smaller list L2 and the bigger list L1 are given:
times(_, 0, []).
times(L2, M, L1) :- append(L2, H, L1), times(L2, N, H), M is N+1.
Seems to work:
?- times([a,b,c],X,[a,b,c,a,b,c]).
X = 2 ;
false.
?- times([a,b,c],X,[a,b,c,a,b,d]).
false.
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