:- object(hill_climbing(Threshold),
instantiates(heuristic_search(Threshold))).
:- info([
version is 1.1,
author is 'Paulo Moura',
date is 2004/8/15,
comment is 'Hill climbing heuristic state space search strategy.',
parnames is ['Threshold']]).
:- uses(list,
[member/2, reverse/2, sort/2]).
:- private(hill/7).
search(Space, State, Threshold, Solution, Cost) :-
hill(Space, State, Threshold, [], Path, 0, Cost),
reverse(Path, Solution).
hill(Space, State, _, Path, [State| Path], Cost, Cost) :-
Space::goal_state(State).
hill(Space, State, Threshold, Path, Solution, SoFar, Total) :-
findall(
(Estimate, Cost, Next),
(Space::next_state(State, Next, Cost),
\+ member(Next, [State| Path]),
Space::heuristic(Next, Guess),
Estimate is Guess + Cost),
States),
sort(States, SortedStates),
member((_, Cost2, Next2), SortedStates),
SoFar2 is SoFar + Cost2,
SoFar2 =< Threshold,
hill(Space, Next2, Threshold, [State| Path], Solution, SoFar2, Total).
:- end_object.
