list of iterators interface implementation

List Of Iterators interface implementation

Question:

A list of iterator, Iterator interface has two function, define a class with the input of a list iterator in the constructor, implement Iterator interface, output in descending order. 

Interface Iterator
{
   HasNext(); 
   Next()
}

List<Iterator<T>>


For example, [1 2] [3 4 5] [7 8], output is [1 2 3 4 5 7 8]



Ideas? 



Do I need to use minimum heap with size of list of iterator? Do I need to use merge k sorted list, using merge sort to lower time complexity O(klogk n)? Do I need to ask more questions on clarification? Each iterator should be sorted in ascending order, for example. 

Many thanks,