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CS261–DataStructures
Linked Lists Variations
List Variations: SortedList
• Sorting doesn’t change the asymptotic time to find an
element since a list only allows sequential access(can’t
jump directlyto the nth element
– But can reduce the time bya factor of 2
• Sorting does help to produce a faster merge sort since
elements can be added in constant time (requires no
temporary data buffer
• The sorted list class is called SortedList?
Sorted List
public class SortedList implements Sorted, Bag, FindMin {
private LinkedList list = new LinkedList();
protected Comparator test;
public SortedList(Comparator t) { test = t; }
public SortedList() { test = new DefaultComparator; }
...
}
•Collection interface handled by the underlying
LinkedList data member
• Much of the Bag interface is also handled by LinkedList
Sorted List: Bag Interface
// Implementation of the Bag interface.
public void addElement(Object obj) {
DoubleLink link = list.head;
while (link != list.tail) {
if (test.compare(obj, link.val) < 0) { // Skip smaller elements.
link.insert(obj);
return;
}
link = link.next
}
link.insert(obj);
}
What’s different?
– LinkedList addElement is O(1)
– What is it for SortedList?
Sorted List: FindMin Interface
The FindMin interface is simple for sorted data:
// Implementation of the FindMin interface.
public Object getFirst() { return list.getFirst(); }
public void removeFirst() { list.removeFirst(); }
Inheritance vs. Composition
Why does SortedList (and SortedVector)use
composition (i.e., it contains a LinkedList (or Vector))
instead of inheriting?
– Both mechanisms create a new abstraction by leveraging an
existing software component
– If the type reduces the numberof operations Æuse composition
– Composition allows objects to be reused whileallowing for
constraints on those aspects (i.e., meth ods and data) you don’t
want accessible by hiding the underlying data structure
– Example: can’t maintain the Sorted property if SortedList
inherits from LinkedList and thus, through inheritance,
implements the Deque interface
