1. Linked Structures – Part 2
COMP 103
Linked Structures – Part 2

2. RECAP-TODAY RECAP TODAY Linked Structures – alternative to arrays
Linked Node (value, reference to next Linked Node)
TODAY
Iterating and printing a linked list
Inserting and deleting in linked lists
Advanced issues for the ‘curious’:
Memory management and Garbage collection in the Java Virtual Machine (page 5 talks about ‘compacting’)
value

3. Using Linked Nodes Making a big list, working forwards:
LinkedNode<Integer> squares = new LinkedNode<Integer>(1, null);
LinkedNode<Integer> last = squares;
for (int i = 2; i < 1000; i++) { last.setNext( new LinkedNode<Integer>(i*i, null) ); last = last.getNext(); } 9 1 4
squares /
last

4. Iterating through a linked list9
LinkedNode<Integer> rest = squares;
while (rest != null) { System.out.printf("%6d \n", rest.get());  rest = rest.next(); } or
for (LinkedNode<Integer> rest=squares; rest!=null; rest=rest.next()) {       System.out.printf("%6d \n", rest.get());
or we could do it with recursion....
squares 4
rest / 1

5. Example: two methods to print out a linked list
/** Print the values in the list starting at a node */
public void printList(LinkedNode<E> list) {
if (list == null) return;
System.out.printf("%s, ", list.get());
printList(list.next()); } or
for (LinkedNode<E> rest=list; rest!=null; rest=rest.next() )
System.out.printf("%s, ", rest.get());
recursive
“cat”
list
“dog”
“cow”
iterative
as per previous slide

6. Example: printList ( the recursive version )
/** Print the values in the list starting at a node */
public void printList(LinkedNode<E> list) {
if (list == null) return;
System.out.printf("%s, ", list.get());
printList(list.next()); }
printList( )
list
cat
dog
cow /
"cat"
dog
cow /
printList( )
calls
(return)
"dog"
cow /
printList( )
calls
(return)
"cow"

7. What about printing the last value?
list
cat
dog
cow /
dog
cow /
lastValue( )
calls
“cow”
cow /
lastValue( )
calls
“cow”

8. Exercise: return the value in the LAST node
/** Return the value in the last node of the list starting at a node */
public E lastValue (LinkedNode<E> list) {
if (list == null) return null; // in case the whole list is empty
if (list.next() == null) return list.get());
return lastValue( list.next() ); } or
if (list == null) return null; // in case the whole list is empty
LinkedNode<E> rest=list;
while (rest.next != null)
rest = rest.next();
return rest.get();
recursive
lastValue( )
cat
dog
cow /
list
iterative

9. Inserting (recursive)
/** Insert the value at position n in the list (counting from 0) Assumes list is not empty, and n>0 */
public void insert (E item, int n, LinkedNode<E>list) {
if (n == 1 )
list.setNext(new LinkedNode<E>(item, list.next());
else
insert(item, n-1, list.next()); }
eg. insert X at position 2 in mylist
recursive
mylist Q W E R T X

10. Inserting (iterative alternative)
/** Insert the value at position n in the list (counting from 0) Assumes list is not empty, and n>0 */
public void insert (E item, int n, LinkedNode<E>list) {
int pos =0;
LinkedNode<E> rest=list; // rest is the pos’th node
while (pos <n-1) {
pos++;
rest=rest.next(); }
rest.setNext(new LinkedNode<E>(item, rest.next());
iterative
mylist Q W E R T

11. Removing (recursive)
/** Remove the value from the list Assumes list is not empty, and value not in first node */
public void remove (E item, LinkedNode<E>list) {
if (list.next() == null) return; // we are at the end of the list
if (list.next().get().equals(item) )
list.setNext( list.next().next());
else
remove(item, list.next()); }
eg. remove R from mylist
eg. remove Q from mylist - ouch: how can I alter mylist??!
recursive W Q R E T
mylist

12. Removing (iterative alternative)or
public void remove (E item, LinkedNode<E>list) {
LinkedNode<E> rest=list;
while (rest.next()!= null && !rest.next().get().equals(item))
rest=rest.next();
if (rest.next()!=null)
rest.setNext(rest.next().next()); }
iterative
NB: two tests

13. Recursion in linked structures
Is this tricky? yes!
we hope you can read the code and see it makes sense
writing it (correctly) is quite hard
just step along and drop off the end (e.g. print all of a list)
look for a node and stop there (e.g. printLast).
look for a node and stop at one before that (e.g. insert, remove)
QUICK TIP: There are three typical patterns