package lrs.visitor;
import lrs.*;

/**
* Sorts by splitting the host into two sublists, sorts the sublists, then
* merges the sorted sublists.
*/
public class MergeSorter implements IAlgo
{
  public static final MergeSorter Singleton = new MergeSorter ();
  private MergeSorter()
  {
  }

	/**
	 * @param host 
	 * @param input not used.
	 * @return null
	 */
	public Object nullCase(LRStruct host, Object input)
	{
		return null;  // there is nothing to sort
	}

	/**
	 * @param host 
	 * @param input not used.
	 * @return null.
	 */
	public Object nonNullCase(LRStruct host, Object input)
	{
    return host.getRest().execute(MergeSortHelper.Singleton, host);
	}
   
	public static void main(String[] args)
	{
      LRStruct l1 = new LRStruct ();
      System.out.println ("l1: " + l1);
      System.out.println ("Merge sort l1...");
      l1.execute(MergeSorter.Singleton, null);
      System.out.println ("l1: " + l1);

      l1.insertFront (new Integer (-9));
      l1.insertFront (new Integer (15));
      l1.insertFront (new Integer (263));
      l1.insertFront (new Integer (-72));
      l1.insertFront (new Integer (0));
      l1.insertFront (new Integer (48));
/*
*/
      System.out.println ("l1: " + l1);
      System.out.println ("Merge sort l1...");
      l1.execute(MergeSorter.Singleton, null);
      System.out.println ("l1: " + l1);
  }
}