CSE116 / CSE504
Introduction to Computer Science II
Dr. Carl Alphonce
343 Davis Hall
alphonce@buffalo.edu
Office hours:
Thursday 12:00 PM – 2:00 PM
Friday 8:30 AM – 10:30 AM
OR request appointment via e-mail
PROFESSIONALISM
Turn off and put away electronics:
cell phones
pagers
laptops
tablets
etc.
© Dr. Carl Alphonce
ROADMAP
Last class
java.util.LinkedList exercise: add
Today
java.util.LinkedList exercise: remove
Wednesday
asymptotic notation
Friday
exam Q&A session (bring questions!)
Exam #2
EXAM INFORMATION
Tuesday 4/12, 9:15 PM - 10:15 PM
Will cover material up to 4/1
If you have a legitimate conflict (work/school):
get documentation, scan it as a PDF
e-mail it to me with subject line:
[CSE116] Exam 2 conflict documentation
NO LATER THAN 5:00 PM on 4/8 (FRIDAY)
A set of sample questions will be posted soon.
WEDNESDAY 4/13 IS EXAM MAKE-UP DAY:
NO REGULAR LECTURE
© Dr. Carl Alphonce
BST OPERATIONS
© Dr. Carl Alphonce
insert(item)
insert into a BST
non-empty case
if ( item < value at root ) {
recursively insert on left
}
else if (item > value at root) {
recursively insert on right
}
else {
// do nothing: duplicate
}
empty case
insert item as root of tree
© Dr. Carl Alphonce
membership in a BST
contains(item)
non-empty case
if ( item < value at root ) {
recursively search in left
}
else if (item > value at root) {
recursively search in right
}
else {
return true;
}
empty case
return false
© Dr. Carl Alphonce
remove from a BST
remove(item)
non-empty case
if ( item < value at root ) {
recursively remove from left
}
else if (item > value at root) {
recursively remove from right
}
else {
remove item
}
empty case
// do nothing: not in tree
© Dr. Carl Alphonce
What’s common?
Each operation traverses the tree structure, to
determine whether a value is already present
in the tree, and if so where, and if not where.
TRAVERSAL!
© Dr. Carl Alphonce
remove(item)
TRAVERSAL
non-empty case
if ( item < value at root ) {
recursively traverse left
}
else if (item > value at root) {
recursively traverse right
}
else {
return tree
}
empty case
return tree
© Dr. Carl Alphonce
insert(item)
TRAVERSE TO RIGHT SPOT, THEN:
insert into a BST
non-empty case
// do nothing: duplicate
empty case
insert item as root of tree
© Dr. Carl Alphonce
membership in a BST
contains(item)
TRAVERSE TO RIGHT SPOT, THEN:
non-empty case
return true;
empty case
return false
© Dr. Carl Alphonce
remove from a BST
remove(item)
TRAVERSE TO RIGHT SPOT, THEN:
non-empty case
remove item
empty case
// do nothing: not in tree
© Dr. Carl Alphonce
Comparable<E>
public interface Comparable<E> {
/* @param
o the object to be compared.
* @return a negative integer, zero, or a positive integer as this object
*
is less than, equal to, or greater than the specified object.
*
* @throws NullPointerException if the specified object is null
* @throws ClassCastException if the specified object's type prevents it
*
from being compared to this object.
*/
public int compareTo(E o);
}
x.compareTo(y) < 0
if x comes before y
x.compareTo(y) == 0 if x and y are at the same place in the order
x.compareTo(y) > 0
if x comes after y
© Dr. Carl Alphonce
TRAVERSAL
public class FindVisitor<E extends Comparable<E>>
implements IAlgo<BRStruct<E>,E,E> {
@Override
public BRStruct<E> emptyCase(BRStruct<E> host, E arg) {
return host;
}
@Override
public BRStruct<E> nonEmptyCase(BRStruct<E> host, E arg) {
if (arg.compareTo(host.getDatum()) < 0) {
return host.getLeft().execute(this, arg);
}
else if (arg.compareTo(host.getDatum()) > 0) {
return host.getRight().execute(this, arg);
}
else {
return host;
}
}
}
© Dr. Carl Alphonce
BST
public class BSTBRStruct<E extends Comparable<E>> {
private BRStruct<E> _brs;
public BSTBRStruct() { _brs = new BRStruct<E>(); }
private final FindVisitor<E> FIND = new FindVisitor<E>();
public BSTBRStruct<E> insert(E item) {
BRStruct<E> tree = _brs.execute(FIND, item);
tree.execute(new IAlgo<Void,E,E>(){
@Override public Void emptyCase(BRStruct<E> host, E item) {
host.insertRoot(item); // item is not in tree, so insert it
return null;
}
@Override public Void nonEmptyCase(BRStruct<E> host, E item) {
return null; // item is already in tree - do not insert again
}
}, item);
return this;
}
public BSTBRStruct<E> remove(E item) {
© Dr. Carl Alphonce
BST
private final RemoveRootVisitor<E> REMOVE = new RemoveRootVisitor<E>();
public BSTBRStruct<E> remove(E item) {
BRStruct<E> tree = _brs.execute(FIND, item);
tree.execute(REMOVE, item);
return this;
}
public boolean member(E item) {
BRStruct<E> tree = _brs.execute(FIND, item);
return tree.execute(new IAlgo<Boolean,E,Void>(){
@Override public Boolean emptyCase(BRStruct<E> host, Void arg) {
return false;
}
@Override public Boolean nonEmptyCase(BRStruct<E> host, Void arg) {
return true;
}
}, null);
}
// REST OF CODE OMITTED
}
© Dr. Carl Alphonce