Notes

package searchmethods;

import agent.Problem;
import agent.Solution;
import agent.State;
import eightpuzzle.EightPuzzleState;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import utils.NodeCollection;

public abstract class GraphSearch<L extends NodeCollection> implements SearchMethod {

protected L frontier;
protected Set<State> explored = new HashSet<State>();
protected Statistics statistics = new Statistics();
protected boolean stopped;
protected EightPuzzleState goalState;

@Override
public Solution search(Problem problem) {
statistics.reset();
stopped = false;
goalState = new EightPuzzleState(EightPuzzleState.goalMatrix);
return graphSearch(problem);
}

/*
function GRAPH-SEARCH(problem) returns a solution, or failure
initialize the frontier using the initial state of problem
initialize the explored set to be empty







*/
protected Solution graphSearch(Problem problem) {

//limpar o frontier
frontier.clear();
frontier.add(new Node(problem.getInitialState()));

explored.clear();

// while(frontier is not empty)
while (!frontier.isEmpty()) {

// remove the first node from the frontier
Node node = frontier.remove();

//if the node contains a goal state then return the corresponding solution
if (problem.isGoal(node.getState(), goalState)) {

return new Solution(problem, node);

}
// add the node to the explored set
explored.add(node.getState());

// expand the node,
List successors = problem.executeActions(node.getState());

// adding the resulting nodes to the frontier only if not in the frontier or explored set
addSuccessorsToFrontier(successors, node);

computeStatistics(successors.size());

}
//return failure
return null;
}

public abstract void addSuccessorsToFrontier(List<State> successors, Node parent);

protected void computeStatistics(int successorsSize) {
statistics.numExpandedNodes++;
statistics.numGeneratedNodes += successorsSize;
statistics.maxFrontierSize = Math.max(statistics.maxFrontierSize, frontier.size());
}

public Statistics getStatistics() {
return statistics;
}

public void stop() {
stopped = true;
}

public boolean hasBeenStopped() {
return stopped;
}

}