TDDC17AICourse/lab2/CustomGraphSearch.java

package searchCustom;

import java.util.ArrayList;
import java.util.HashSet;

import searchShared.NodeQueue;
import searchShared.Problem;
import searchShared.SearchObject;
import searchShared.SearchNode;

import world.GridPos;

public class CustomGraphSearch implements SearchObject {

	private HashSet<SearchNode> explored;
	private NodeQueue frontier;
	protected ArrayList<SearchNode> path;
	private boolean insertFront;

	/**
	 * The constructor tells graph search whether it should insert nodes to front or back of the frontier 
	 */
    public CustomGraphSearch(boolean bInsertFront) {
		insertFront = bInsertFront;
    }

	/**
	 * Implements "graph search", which is the foundation of many search algorithms
	 */
	public ArrayList<SearchNode> search(Problem problem) {
		// The frontier is a queue of expanded SearchNodes not processed yet
		frontier = new NodeQueue();
		// The explored set is a set of nodes that have been processed 
		explored = new HashSet<SearchNode>();
		// The start state is given
		GridPos startState = (GridPos) problem.getInitialState();
		// Initialise the frontier with the start state  
		frontier.addNodeToFront(new SearchNode(startState));

		// Path will be empty until we find the goal.
		path = new ArrayList<SearchNode>();
		
		
		/*
		 * Note on how java and this program work:
		 *  -ArrayList are just resizable array. "<>" contains the type of the listed objects
		 *  -Structures :
		 *  	while (boolean) {}
		 *  	while (a > 0) {}
		 *  	for (int i = 0; i < 5; i++){}		--> 5 iterations
		 *  	for (String i : StringList){}		--> Iterations on all the objects in the list
		 *  -Class used here:
		 *  	-SearchNode					--> Equivalent of the "Node" class in the Python program. Represent a node.
		 *  	-Problem 					--> Class containing lot of informations on the problem
		 *  									like the reachable states from a position, the start, the end
		 *  	-GridPos 					--> represent a position (with x and y coordinates)  	
		 */
		
		
		// While we have something to explore
		while (frontier.size() > 0) {
			// Get the first node on the list
			SearchNode Node = frontier.removeFirst();
			
			// We check if it is our destination
			if (problem.isGoalState(Node.getState())) {
				return path = Node.getPathFromRoot();
			} // if not, we continue
			
			// Get the list of children of the current node
			ArrayList<GridPos> childPosition = problem.getReachableStatesFrom(Node.getState());
			// For every child in the list
			for (GridPos position : childPosition) {
				// Creating a new node
				SearchNode childNode = new SearchNode(position, Node);
				// If we have not explored the node
				if (explored.contains(childNode) == false) {
					// Adding the child node to the frontier
					// Front --> DFS (LIFO queue)
					// Back --> BFS (FIFO queue)
					if (insertFront) {
						frontier.addNodeToFront(childNode);
					}
					else {
						frontier.addNodeToBack(childNode);
					}
					// We add the node to explored node
					explored.add(childNode);
				}
			}
		}
		
		
		/* Some hints:
		 * -Read early part of chapter 3 in the book!
		 * -You are free to change anything how you wish as long as the program runs, but some structure is given to help you.
		 * -You can Google for "javadoc <class>" if you are uncertain of what you can do with a particular Java type.
		 * 
		 * -SearchNodes are the nodes of the search tree and contains the relevant problem state, in this case x,y position (GridPos) of the agent 
		 * --You can create a new search node from a state by: SearchNode childNode = new SearchNode(childState, currentNode);
		 * --You can also extract the state by .getState() method
		 * --All search structures use search nodes, but the problem object only speaks in state, so you may need to convert between them 
		 * 
		 * -The frontier is a queue of search nodes, open this class to find out what you can do with it! 
		 * 
		 * -If you are unfamiliar with Java, the "HashSet<SearchNode>" used for the explored set means a set of SearchNode objects.
		 * --You can add nodes to the explored set, or check if it contains a node!
		 * 
		 * -To get the child states (adjacent grid positions that are not walls) of a particular search node, do: ArrayList<GridPos> childStates = p.getReachableStatesFrom(currentState);
		 * 
		 * -Depending on the addNodesToFront boolean variable, you may need to do something with the frontier... (see book)
		 * 
		 * -You can check if you have reached the goal with p.isGoalState(NodeState)
		 * 
		 *  When the goal is found, the path to be returned can be found by: path = node.getPathFromRoot();
		 */
		/* Note: Returning an empty path signals that no path exists */
		return path;
	}

	/*
	 * Functions below are just getters used externally by the program 
	 */
	public ArrayList<SearchNode> getPath() {
		return path;
	}

	public ArrayList<SearchNode> getFrontierNodes() {
		return new ArrayList<SearchNode>(frontier.toList());
	}
	public ArrayList<SearchNode> getExploredNodes() {
		return new ArrayList<SearchNode>(explored);
	}
	public ArrayList<SearchNode> getAllExpandedNodes() {
		ArrayList<SearchNode> allNodes = new ArrayList<SearchNode>();
		allNodes.addAll(getFrontierNodes());
		allNodes.addAll(getExploredNodes());
		return allNodes;
	}

}