Algorithm of Finding the Lost keys

package schildt.herbert;
 
/*
 * 
 * Chapter 10 - AI-Based Problem Solving The Art of Java by Herbert Schildt and
 * James Holmes McGraw-Hill/Osborne 2003
 */
 
import java.util.Stack;
 
//Room information.
class RoomInfo {
    String from;
 
    String to;
 
    boolean skip;
 
    RoomInfo(String f, String t) {
	from = f;
	to = t;
	skip = false;
    }
}
 
public class Keys {
    final int MAX = 100;
 
    // This array holds the room information.
    RoomInfo room[] = new RoomInfo[MAX];
 
    int numRooms = 0; // number of rooms
 
    Stack btStack = new Stack(); // backtrack stack
 
    public static void main(String args[]) {
	String to, from;
	Keys ob = new Keys();
 
	ob.setup();
 
	from = "front_door";
	to = "keys";
 
	ob.iskeys(from, to);
 
	if (ob.btStack.size() != 0)
	    ob.route(to);
    }
 
    // Initialize the room database.
    void setup() {
	addRoom("front_door", "lr");
	addRoom("lr", "bath");
	addRoom("lr", "hall");
	addRoom("hall", "bd1");
	addRoom("hall", "bd2");
	addRoom("hall", "mb");
	addRoom("lr", "kitchen");
	addRoom("kitchen", "keys");
    }
 
    // Put rooms into the database.
    void addRoom(String from, String to) {
	if (numRooms < MAX) {
	    room[numRooms] = new RoomInfo(from, to);
	    numRooms++;
	} else
	    System.out.println("Room database full.\n");
    }
 
    // Show the route.
    void route(String to) {
	Stack rev = new Stack();
	RoomInfo r;
	int num = btStack.size();
 
	// Reverse the stack to display path.
	for (int i = 0; i < num; i++)
	    rev.push(btStack.pop());
 
	for (int i = 0; i < num; i++) {
	    r = (RoomInfo) rev.pop();
	    System.out.print(r.from + " to ");
	}
 
	System.out.println(to);
    }
 
    /*
     * If there is a path between from and to, return true, otherwise return false.
     */
    boolean match(String from, String to) {
	for (int i = numRooms - 1; i > -1; i--) {
	    if (room[i].from.equals(from) && room[i].to.equals(to) && !room[i].skip) {
		room[i].skip = true; // prevent reuse
		return true;
	    }
	}
 
	return false; // not found
    }
 
    // Given from, find any path.
    RoomInfo find(String from) {
	for (int i = 0; i < numRooms; i++) {
	    if (room[i].from.equals(from) && !room[i].skip) {
		RoomInfo r = new RoomInfo(room[i].from, room[i].to);
		room[i].skip = true; // prevent reuse
 
		return r;
	    }
	}
	return null;
    }
 
    // Determine if there is a path between from and to.
    void iskeys(String from, String to) {
	int dist;
	RoomInfo r;
 
	// See if at destination.
	if (match(from, to)) {
	    btStack.push(new RoomInfo(from, to));
	    return;
	}
	// Try another connection.
	r = find(from);
	if (r != null) {
	    btStack.push(new RoomInfo(from, to));
	    iskeys(r.to, to);
	} else if (btStack.size() > 0) {
	    // Backtrack and try another connection.
	    r = (RoomInfo) btStack.pop();
	    iskeys(r.from, r.to);
	}
    }
}