Predicate to match list (all possibilities) with no duplicate integers, have length N, and be within a domain of 1 to N
This is for GNU-Prolog
I'm having trouble getting a certain predicate to work. Its functionality is that it matches a list of integers
that have a domain of 1 to N
with no duplicates and length N
. Basically what I want to do is have this as inputs and outputs:
| ?- row_valid(X, 3).
X = [1, 2, 3] ? ;
X = [1, 3, 2] ? ;
X = [2, 1, 3] ? ;
X = [2, 3, 1] ? ;
X = [3, 1, 2] ? ;
X = [3, 2, 1] ? ;
no
| ?- row_valid(X, 2).
X = [1, 2] ? ;
X = [2, 1] ? ;
no
| ?- row_valid(X, 1).
X = [1] ? ;
no
But right now, this is what is happening:
| ?- row_valid(X, 3).
X = [] ? ;
no
This is probably happening because of the row_valid([], _).
predicate I have in the code. However, I can verify that the predicate matches correctly since:
| ?- row_valid([1,2,3], 3).
true ?
yes
Here are the predicates defined. Do you have any suggestions on how I could get this to work the way I want? Thanks for your time.
% row_valid/2: matches if list of integers has domain of 1 to N and is not duplicated
% 1 - list of integers
% 2 - N
row_valid([], _).
row_valid(Row, N) :-
length(Row, N), % length
no_duplicates_within_domain(Row, 1, N),
row_valid(RestRow, N).
% no_duplicates/1: matches if list doesn't have repeat elements
% 1 - list
no_duplicates([]). % for empty list always true
no_duplicates([Element | RestElements]) :-
\+ member(Element, RestElements), % this element cannot be repeated in the list
no_duplicates(RestElements).
% within_domain/3 : matches if list integers are within a domain
% 1 - list
% 2 - m开发者_开发知识库in
% 3 - max
within_domain(Integers, Min, Max) :-
max_list(Integers, Max),
min_list(Integers, Min).
% no_duplicates_within_domain/3: matches if list integers are within a domain and isn't repeated
% 1 - list
% 2 - min
% 3 - max
no_duplicates_within_domain(Integers, Min, Max) :-
no_duplicates(Integers),
within_domain(Integers, Min, Max).
How about the following?
row_valid(Xs,N) :-
length(Xs,N),
fd_domain(Xs,1,N),
fd_all_different(Xs),
fd_labeling(Xs).
Running it with GNU Prolog 1.4.4:
?- row_valid(Xs,N).
N = 0
Xs = [] ? ;
N = 1
Xs = [1] ? ;
N = 2
Xs = [1,2] ? ;
N = 2
Xs = [2,1] ? ;
N = 3
Xs = [1,2,3] ? ;
N = 3
Xs = [1,3,2] ? ;
N = 3
Xs = [2,1,3] ? ;
N = 3
Xs = [2,3,1] ? ;
N = 3
Xs = [3,1,2] ? ;
N = 3
Xs = [3,2,1] ? ;
N = 4
Xs = [1,2,3,4] ? % ...and so on...
Here is a simple piece of code that does this in SWI-Prolog. I don't know if GNU-Prolog provides between/3
and permutation/2
, so maybe it doesn't directly answer your question, but maybe it can still help you further.
row_valid(List, N) :-
findall(X, between(1, N, X), Xs),
permutation(Xs, List).
Usage examples:
?- row_valid(List, 0).
List = [].
?- row_valid(List, 1).
List = [1] ;
false.
?- row_valid(List, 2).
List = [1, 2] ;
List = [2, 1] ;
false.
?- row_valid(List, 3).
List = [1, 2, 3] ;
List = [2, 1, 3] ;
List = [2, 3, 1] ;
List = [1, 3, 2] ;
List = [3, 1, 2] ;
List = [3, 2, 1] ;
false.
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