AverageAverage.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class AverageAverage {

	
	/* 
	 * perm []      = [[]]
     * perm (x:xs)  =  (list ++  (map (x:)  list))
     *      where list = (perm xs)
	 */
	public List<List<Integer>> permutaions(List<Integer> seq)
	{
		List<List<Integer>> result = new ArrayList<List<Integer>>();
		List<Integer> list = new ArrayList<Integer>();
		
		if (seq.isEmpty())
		{
			result.add(list);
			return result;
		}
		else
		{
			List<Integer> seq2 = new ArrayList<Integer>();			
			for (Integer n : seq)
			{
				seq2.add(n);
			}				
			Integer a = seq2.get(0);

			seq2.remove(0);			
			List<List<Integer>> list2 = permutaions(seq2);
			List<List<Integer>> list3 = permutaions(seq2);
			for (List<Integer> l :list3)
			{
				l.add(a);
			}
			
			for (List<Integer> l :list2)
			{
				result.add(l);
			}			
			
			for (List<Integer> l :list3)
			{
				result.add(l);
			}
		}
		return result;
	}
	
	public Integer sum(List<Integer> seq)
	{
		Integer sum =0;
		for(Integer n: seq)
		{
			sum+=n;
		}
		return sum;
	}
	
	public double average(int[] numList) 
	{
		List<Integer> list = new ArrayList<Integer>();
		for(int i=0 ; i<numList.length ; i++)
		{
			list.add(numList[i]);
		}
		
		
		double sum=0.0;
		double length = 0.0;
		for (List<Integer> xs : permutaions(list))
		{
			if (!xs.isEmpty())
			{
				length += 1.0;
				int len = xs.size();
				sum += ((double)sum(xs)/(double)len);
			}						
		}
		double average = sum/length;
		
		System.out.println(average);
		return average;
	}

}