:- use_module(contestlib, [for/3]).

remote(Channels,Zaps) :- once(gen_shortest(Channels,Zaps)).

gen_shortest(Channels,Zaps) :-
	LastZapped = none,
	length(Zaps,_),
	gen_allowed_zapping(Zaps,LastZapped),
	check_zaps(Zaps,Channels,[X,X,X,X]).

gen_allowed_zapping([],_).
gen_allowed_zapping([Zap|Zaps],LastZapped) :-
	for(Zap,1,5),
	Zap \== LastZapped,
	gen_allowed_zapping(Zaps,Zap).

check_zaps([],Channels,Channels).
check_zaps([Zap|Zaps],ChannelsIn,ChannelsOut) :-
	zap(Zap,ChannelsIn,Channels1),
	check_zaps(Zaps,Channels1,ChannelsOut).

zap(1,[A,B,C,D],[A1,B,C,D]) :- zap(A,A1).
zap(2,[A,B,C,D],[A,B1,C,D]) :- zap(B,B1).
zap(3,[A,B,C,D],[A,B,C1,D]) :- zap(C,C1).
zap(4,[A,B,C,D],[A,B,C,D1]) :- zap(D,D1).

zap(X,Y) :- Y is (X mod 5) + 1.