Question

How to complete this JAVA method?
public static <E> AttachedList<AttachedList<E>> pack(AttachedList<E> flatList) {
   //given a 1D (flatList), "pack" sequential items together
   //to form a 2D list of values

   //Example 1: [1,1,2,3,3] becomes [[1,1],[2],[3,3]]
   //Example 1: [1,1,2,1,1,2,2,2,2] becomes [[1,1],[2],[1,1],[2,2,2,2]]
   //Example 3: [1,2,3,4,5] becomes [[1],[2],[3],[4],[5]]
   //IMPORTANT: the above examples are _lists NOT arrays_

   //promise: we will never test this with nulls in the flatList
   //though there's no harm in coding it to work with nulls
}

Answer 1

public static <E> AttachedList<AttachedList<E>> pack(AttachedList<E> flatList) {

   AttachedList<AttachedList<E>> result = new AttachedList<>();
   E lastItem;
   AttachedList<E> lastList = new AttachedList<>();
   
   
   for(int i=0; i<flatList.size(); i++) {
                E item = flatList.get(i);
                
                if(i == 0) {
                        lastItem = item;
                        lastList.add(item);
                } else {
                        if(item.equals(lastItem)) {
                                lastList.add(item);
                        } else {
                                result.add(lastList);
                                lastList = new AttachedList<>();
                                lastList.add(item);
                        }
                        lastItem = item;
                }               
   }
   
   if(lastList.size() != 0) {
                result.add(lastList);
   }
   return result;
}

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You have not given the code for AttachedList class, So i can not really test the code.. 

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