PermutationHelper.java

package hu.bme.mit.incquery.cep.performance.test.generator;

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

import com.google.common.collect.Lists;

public class PermutationHelper<E> {
	public List<List<E>> generatePerm(List<E> original) {
		if (original.size() == 0) {
			List<List<E>> result = new ArrayList<List<E>>();
			result.add(new ArrayList<E>());
			return result;
		}
		E firstElement = original.remove(0);
		List<List<E>> returnValue = new ArrayList<List<E>>();
		List<List<E>> permutations = generatePerm(original);
		for (List<E> smallerPermutated : permutations) {
			for (int index = 0; index <= smallerPermutated.size(); index++) {
				List<E> temp = new ArrayList<E>(smallerPermutated);
				temp.add(index, firstElement);
				returnValue.add(temp);
			}
		}
		return returnValue;
	}
	
	public List<List<E>> generatePerm2(List<E> original, int length) {
		if (original.size() == 0) {
			List<List<E>> result = new ArrayList<List<E>>();
			result.add(new ArrayList<E>());
			return result;
		}
		E firstElement = original.remove(0);
		List<List<E>> returnValue = new ArrayList<List<E>>();
		List<List<E>> permutations = generatePerm(original);
		int i = 0;
		for (List<E> smallerPermutated : permutations) {
			for (int index = 0; index <= smallerPermutated.size(); index++) {
				System.out.println(i);
				if(i==length){
					return returnValue;
				}
				List<E> temp = new ArrayList<E>(smallerPermutated);
				temp.add(index, firstElement);
				returnValue.add(temp);
				i++;
			}
		}
		return returnValue;
	}
}