Java - Permutation of ArrayList elements (Integer) - Can't get it to work properly

Question

I\'ve been looking around quite a bit to solve my issue. I got many problems solved but this one is still haunting me :S It\'s been a long time I haven\'t touch Java program

Answer 1

Try this, it seems to work, it uses recursion.

public class Permute {

    public static List> permute(Integer...myInts){

        if(myInts.length==1){
            List arrayList = new ArrayList();
            arrayList.add(myInts[0]);
            List > listOfList = new ArrayList>();
            listOfList.add(arrayList);
            return listOfList;
        }

        Set setOf = new HashSet(Arrays.asList(myInts));   

        List> listOfLists = new ArrayList>();

        for(Integer i: myInts){
            ArrayList arrayList = new ArrayList();
            arrayList.add(i);

            Set setOfCopied = new HashSet();
            setOfCopied.addAll(setOf);
            setOfCopied.remove(i);

            Integer[] isttt = new Integer[setOfCopied.size()];
            setOfCopied.toArray(isttt);

            List> permute = permute(isttt);
            Iterator> iterator = permute.iterator();
            while (iterator.hasNext()) {
                List list = iterator.next();
                list.add(i);
                listOfLists.add(list);
            }
        }   

        return listOfLists;
    }

    public static void main(String[] args) {
        List> permute = permute(1,2,3,4);
        System.out.println(permute);
    }

}

If you don't like the List> you can easily change from arrays to list using the methods from list and static methods from java.util.Collections and java.util.Arrays.