Permutations: Difference between revisions

</lang>

=={{header|Mercury}}==

<lang mercury>

:- module permutations2.

:- interface.

:- import_module io.

:- pred main(io::di, io::uo) is det.

:- import_module list.

:- import_module set_ordlist.

:- import_module set.

:- import_module solutions.

%% permutations(List, Set) is true if List is a permutation of Set:

:- pred permutationSet(list(A)::out,set(A)::in) is nondet.

%% Two ways to compute all permutations of a given list (using backtracking):

:- func all_permutations1(list(int))=set_ordlist.set_ordlist(list(int)).

:- func all_permutations2(list(int))=set_ordlist.set_ordlist(list(int)).

:- implementation.

permutationSet([],set.init).

permutationSet([H|T], S) :- set.member(H,S), permutationSet(T,set.delete(S,H)).

all_permutations1(L) =

solutions_set(pred(X::out) is nondet:-permutationSet(X,set.from_list(L))).

all_permutations2(L) =

solutions_set(pred(X::out) is nondet:-perm(L,X)).

main(!IO) :-

print(all_permutations1([1,2,3,4,5]),!IO),

nl(!IO),

print(all_permutations2([1,2,3,4,5]),!IO).