aima.core.search.framework

Class Node

java.lang.Object

aima.core.search.framework.Node

public class Node
extends java.lang.Object

Artificial Intelligence A Modern Approach (3rd Edition): Figure 3.10, page 79.
Figure 3.10 Nodes are the data structures from which the search tree is constructed. Each has a parent, a state, and various bookkeeping fields. Arrows point from child to parent.

Search algorithms require a data structure to keep track of the search tree that is being constructed. For each node n of the tree, we have a structure that contains four components:

• n.STATE: the state in the state space to which the node corresponds;
• n.PARENT: the node in the search tree that generated this node;
• n.ACTION: the action that was applied to the parent to generate the node;
• n.PATH-COST: the cost, traditionally denoted by g(n), of the path from the initial state to the node, as indicated by the parent pointers.

Author:

Ravi Mohan, Ciaran O'Reilly, Mike Stampone

Constructor Summary

Constructors

Constructor and Description
Node(java.lang.Object state) Constructs a node with the specified state.
Node(java.lang.Object state, Node parent, Action action, double pathCost) Constructs a node with the specified state, parent, action, and path cost.

Method Summary

Modifier and Type	Method and Description
Action	getAction() Returns the action that was applied to the parent to generate the node.
Node	getParent() Returns this node's parent node, from which this node was generated.
double	getPathCost() Returns the cost of the path from the initial state to this node as indicated by the parent pointers.
java.util.List<Node>	getPathFromRoot() Returns the path from the root node to this node.
java.lang.Object	getState() Returns the state in the state space to which the node corresponds.
boolean	isRootNode() Returns true if the node has no parent.
java.lang.String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Node

public Node(java.lang.Object state)

Constructs a node with the specified state.

Parameters:

state - the state in the state space to which the node corresponds.

Node

public Node(java.lang.Object state,
            Node parent,
            Action action,
            double pathCost)

Constructs a node with the specified state, parent, action, and path cost.

Parameters:

state - the state in the state space to which the node corresponds.

parent - the node in the search tree that generated the node.

action - the action that was applied to the parent to generate the node.

pathCost - full pathCost from the root node to here, typically the root's path costs plus the step costs for executing the the specified action.

Method Detail

getState

public java.lang.Object getState()

Returns the state in the state space to which the node corresponds.

Returns:

the state in the state space to which the node corresponds.

getParent

public Node getParent()

Returns this node's parent node, from which this node was generated.

Returns:

the node's parenet node, from which this node was generated.

getAction

public Action getAction()

Returns the action that was applied to the parent to generate the node.

Returns:

the action that was applied to the parent to generate the node.

getPathCost

public double getPathCost()

Returns the cost of the path from the initial state to this node as indicated by the parent pointers.

Returns:

the cost of the path from the initial state to this node as indicated by the parent pointers.

isRootNode

public boolean isRootNode()

Returns true if the node has no parent.

Returns:

true if the node has no parent.

getPathFromRoot

public java.util.List<Node> getPathFromRoot()

Returns the path from the root node to this node.

Returns:

the path from the root node to this node.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object