java.util.ConcurrentModificationException & iteration?

Question

I\'m so very new to Arraylists & iterators & this is the first time I got this exception. I have an ArrayList u & I\'d like to do the following algorithm:

Answer 1

Try this:

Iterator iter = u.iterator();
while (iter.hasNext())
{
    Character currentChar = iter.next();

    if(k==1){           //base case

        if(isAnswer(s+u.get(0)))

        System.out.println(s+u.get(0)+" is the correct sequence."+ '\n');
        return;
    }

    else{
         iter.remove();
         puzzleSolve(k-1, s+currentChar  , u);
         u.add(currentChar);
         removeLastChar(s);
    }

}