package cc.mallet.util.search;
import java.util.Iterator;
/**
* Created by IntelliJ IDEA.
* User: pereira
* Date: Jun 20, 2005
* Time: 4:46:56 PM
*
* Search tree node. A search tree node pertains to some search graph state.
* Multiple nodes may refer to the same state, representing different ways
* of reaching the state. Search nodes have a priority, which determines when
* they will be expanded, and cost of reaching the node from the start of the
* search.
*/
public class SearchNode implements QueueElement {
private int position = -1;
private double priority = Double.POSITIVE_INFINITY;
private double cost;
private SearchNode parent;
private SearchState state;
/**
* This iterator generates search nodes that refer to the
* states reachable from the state pertaining to a this search node.
*/
public class NextNodeIterator implements Iterator {
private SearchState.NextStateIterator stateIter;
protected NextNodeIterator() {
stateIter = state.getNextStates();
}
public boolean hasNext() { return stateIter.hasNext(); }
public Object next() { return nextNode(); };
/**
* The search tree node for the next state reached from
* the current state.
* @return a new search tree node
*/
public SearchNode nextNode() {
SearchNode p = SearchNode.this;
SearchState s = stateIter.nextState();
return new SearchNode(s, p, p.getCost() + cost());
}
/**
* The cost associated to the transition from the previous
* state to this state.
* @return the cost
*/
public double cost() { return stateIter.cost(); }
public void remove() {
throw new UnsupportedOperationException();
}
protected SearchState.NextStateIterator getStateIter() {
return stateIter;
}
}
/**
* Create a search node with given state, parent, and cost.
* @param state the state
* @param parent the parent
* @param cost the cost
*/
public SearchNode(SearchState state, SearchNode parent, double cost) {
this.state = state;
this.parent = parent;
this.cost = cost;
}
public double getPriority() { return priority; }
public void setPriority(double priority) { this.priority = priority; }
public int getPosition() { return position; }
public void setPosition(int position) { this.position = position; }
/**
* The node that generated this node.
* @return the parent
*/
public SearchNode getParent() { return parent; }
/**
* Get the cost for this node.
* @return the cost
*/
public double getCost() { return cost; }
/**
* The state for this search node.
* @return the state
*/
public SearchState getState() { return state; }
/**
* Is the node's state final?
* @return whether this state's node is final
*/
public boolean isFinal() { return state.isFinal(); }
/**
* Get an iterator over the new search nodes reachable
* from this node by state transitions.
* @return the iterator
*/
public NextNodeIterator getNextNodes() {
return new NextNodeIterator();
}
public String toString() {
return state.toString() + "/" + priority;
}
}