QuickSort.java

package sort;

import java.util.ArrayList;

import com.hygenics.comparator.CompareObjects;


/**
 * Generic general purpose QuickSort. Sorts any list. O(nlogn) or O(n^2) but 
 * can run smaller data better than heap or merge sorts.
 * 
 * @author asevans
 *
 * @param <E>
 */
public class QuickSort<E>{
	
	private ArrayList<E> tosortlist;

	private CompareObjects<E> comparator=new CompareObjects<E>();
	

	
	public QuickSort(){
		
	}
	
	

	public ArrayList<E> getTosortlist() {
		return tosortlist;
	}


	public void setTosortlist(ArrayList<E> tosortlist){
		//sort list
		this.tosortlist = tosortlist;
	}

	/**
	 * Exchange two positions
	 */
	private void exchange(int newhigh, int newlow){
		//TODO exchange positions in our list
		E temp=tosortlist.get(newhigh);
		tosortlist.set(newhigh, tosortlist.get(newlow));
		tosortlist.set(newlow, temp);
		temp=null;
	}

	/**
	 * Perform the quicksort
	 * @param high
	 * @param low
	 */
	private void run(int high, int low){
		//TODO run the quicksort
		
		int newhigh=high;
		int newlow=low;
		int pivot=(int)Math.ceil((low + high)/2);
		
		while(newlow <= newhigh){
			
			//get the splits
			while(newhigh > 0 & comparator.compare(tosortlist.get(newhigh),tosortlist.get(pivot))==1){
				newhigh--;
			}
		
			while(newlow < (tosortlist.size()-1) & comparator.compare(tosortlist.get(newlow),tosortlist.get(pivot))==-1)
			{		
				newlow++;
			}
			
			
			if(newlow<=newhigh){
				exchange(newhigh,newlow);
				newlow++;
				newhigh--;
			}
			
			//recursively get new list
			 if (low < newhigh){
			      run(newhigh,low);
			 }
			 
			 if (newlow < high){
			    run(high,newlow);
			 }
		}
	}
	
	
	/**
	 * Run the quicksort
	 */
	private ArrayList<E> run(){

		run((tosortlist.size()-1),0);
		//return our new sorted list
		return tosortlist;
	}
	
	/**
	 * Perform the sort
	 * @return
	 */
	public ArrayList<E> sort(){
		
		if(tosortlist==null){
			try{
				throw new NullPointerException("No List to QuckSort!");
			}catch(NullPointerException e)
			{
				e.printStackTrace();
			}
		}
		else if(tosortlist.size()<2)
		{
			return tosortlist;
		}
		
		return run();
	}
	

}