/*
 * Created on Mar 31, 2004
 *  
 */
package eightPuzzle;

import java.util.Hashtable;

/**
 * @author kgajos
 * 
 * Data structure to keep track of previously visited nodes
 */
public class ClosedList {

  // storing the nodes; the mapping is from boards to boards
  // -- it is weird but it was the fastest way to not only check
  // if an element exists in the closed list but also pull out
  // the old instance
  protected Hashtable nodes = new Hashtable();

  /**
   *  Creates an instance of the ClosedList
   */
  public ClosedList() {}

  public void add(Board board) {
    nodes.put(board, board);
  }
	
  /**
   * Checks if the closed list contains a board that looks just like
   * the one passed as an argument
   * 
   * @param board reference board
   * @return true if an identical board exists; false otherwise
   */	
  public boolean contains(Board board) {
    return nodes.contains(board);
  }
	
  /**
   * returns the cost estimate for the stored instance of this
   * board configuration
   * 
   * @param board a board configuration to be checked
   * @return the stored cost estimate or -1 if the board state
   * is not in the closed list
   */
  public int getCostFor(Board board) {
    if (contains(board))
      return ((Board)nodes.get(board)).getCostEstimate();
    return -1;
  }
	
  /**
   * Removes the board (or one that looks like it) from the closed
   * list
   * 
   * @param board board to be removed
   */
  public void remove(Board board) {
    nodes.remove(board);
  }
	
}