List and Binary Tree Iterator...

List and Binary Tree Iterator ImplementationLecture 35

Section 14.6

Robb T. Koether

Hampden-Sydney College

Fri, Apr 26, 2013

Robb T. Koether (Hampden-Sydney College) List and Binary Tree Iterator Implementation Fri, Apr 26, 2013 1 / 35

1 LinkedList Iterators

2 List Traversals

3 Reverse Iterators

4 Binary Tree IteratorsPreorder IteratorsInorder IteratorsPostorder Iterators

5 Assignment

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

A Sort Function

Sorting with Iteratorsvoid LinkedListwIter<T>::sortIter(){

Iterator base = begin();while (base != end()){

Iterator min = base;Iterator curr = min;++curr;while (curr != end()){

if (*curr < *min)min = curr;

++curr;}T temp = *base;

*base = *min;

*min = temp;++base;

}return;

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

List Traversals

Definition (Traverse)To traverse a list is to move systematically through its nodes, “visiting”each node along the way. Forward traversals go from head to tail.Reverse traversals go from tail to head.

The meaning of “visiting” a node is left unspecified at this point.The meaning will be specified at the time of the traversal.

The Traversal Function

The traverse() Functionvoid traverse(void (*visit)(Iterator&));

Introduce a new List member function traverse().The parameter visit is a pointer to a function.The visit() function has prototype

void visit(Iterator& it);

Traversals and Iterators

Traversal Implementationvoid traverse(void (*visit)(Iterator&)){

for (Iterator it = begin(); it != end(); ++it)visit(it);

return;}

The traverse() function is implemented as a for loop.

Example - Print the List

The print() Functionvoid print(Iterator& it){

cout << *it << endl;return;

list.traverse(print);

For example, we could write a print() function and then usetraverse() to print all the values in the list.

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Reverse Iterators

A reverse iterator is an iterator that advances in the oppositedirection, from tail to head.It is initialized to the last element in the list.It “advances” until it has gone beyond the head of the list.Because a reverse iterator is an iterator, we will derive theReverseIterator class from the Iterator class.

ReverseIterator Member Functions

Additional ReverseIterator Member FunctionsReverseIterator(const LinkedListwIter<T>* lst,

LinkedListNode<T>* p);ReverseIterator& operator++();

ReverseIterator(LinkedListwIter<T>*,LinkedListNode<T>*) – Construct a ReverseIterator.operator++() – Advance the ReverseIterator to the nextnode.

LinkedListwIter Member Functions

Additional LinkedListwIter Member FunctionsReverseIterator rbegin() const;ReverseIterator rend() const;

rbegin() – Create a ReverseIterator set to the beginning(tail) of the list.rend() – Create a ReverseIterator set to the end (beyondthe head) of the list.

LinkedListwIter Member Functions

The other LinkedListwIter member functions that useiterators, such as the iterator version of getElement(), canaccept reverse iterators as well because. . .That is because

A ReverseIterator IS-A Iterator.

Implemention of Reverse Iterators

To construct a reverse iterator for a linked list,Introduce a stack data member.Push NULL onto the stack.Then push the addresses of the nodes onto the stack as the list istraversed from head to tail.Stop with all but the final NULL pointer on the stack.Now the reverse iterator is initialize.

To increment the reverse list iteratorPop an address off the stack.Assign it to the node pointer.

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Binary Tree Iterators

In a list, we could traverse in only two ways:Head to tail (forward)Tail to head (reverse)

In a binary tree, there is a variety of ways in which we can traversethe structure.

Pre-orderIn-orderPost-orderLevel-order, etc.

Accordingly, we create the following binary tree iterator classes.PreorderIterator classInorderIterator classPostorderIterator classLevelorderIterator class

Furthermore, these are all subclasses of a base class Iterator.By using inheritance, all we have to implement for each subclassis

The constructor.The ++ operator.

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Binary Tree Preorder Iterators

We will build on what we learned about reverse iterators for lists.To reach the “next” node from a root node, a preorder iterator mustmove to the root of the left subtree.It should also push the pointer to the right subtree, if there is one.

The binary tree

Visit root node, push null pointer

Push pointer to right subtree, move left

Pop pointer, visit node

Pop null pointer, quit

Preorder Iterator ConstructorPreorderIterator(const BinaryTree<T>* bt,

BinaryTreeNode<T>* rt) : Iterator(bt, rt){

stack.push(NULL);return;

Preorder Iterator operator++()PreorderIterator& operator++(){

if (node != NULL){

if (node->rightNode() != NULL)stack.push(node->rightNode());

if (node->leftNode() != NULL)node = node->leftNode();

elsenode = stack.pop();

}return *this;

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Binary Tree Inorder Iterators

To reach the “next” node from a root node, an inorder iterator musttravel to the right subtree, and then as far left as possible, pushingnode pointers along the way.

The binary tree

Start at root node, push null pointer

Push pointer to node, move left

Visit node

Move right

Visit node

Inorder Iterator ConstructorInorderIterator(const BinaryTree<T>* bt,

stack.push(NULL);if (node != NULL)

while (node->leftNode() != NULL){

stack.push(node);node = node->leftNode();

}return;

Inorder Iterator operator++()InorderIterator& operator++(){

if (node != NULL){

if (node->rightNode() != NULL){

node = node->rightNode();while (node->leftNode() != NULL){

stack.push(node);node = node->leftNode();

}}else

node = stack.pop();}return *this;

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Binary Tree Postorder Iterators

To the “next” node from a root node, a postorder iterator must dothe following.If the current node is a left child, then the iterator must followingthe leftmost branch of the sibling right subtree all the way to a leafnode, pushing nodes along the way.

The binary tree

p9 NULL

Start at root node, push null pointer

p9 NULL

Push pointer to node, move right

p9 NULL

Visit node

p9 NULL

Move to right child of parent, visit node

p9 NULL

Move to right child of parent

Push pointer to node, move left, visit node

p9 NULL

Pop pointer, visit that node

p9 NULL

Postorder Iterator ConstructorPostorderIterator(const BinaryTree<T>* bt,

stack.push(NULL);if (node != NULL)

while (node->leftNode() != NULL|| node->rightNode() != NULL){

stack.push(node);if (node->leftNode() != NULL)

node = node->leftNode();else

node = node->rightNode();}

return;}

Postorder Iterator operator++()PostorderIterator& operator++(){

if (node != NULL){

BinaryTreeNode<T>* parent = stack.top();if (parent != NULL && node == parent->leftNode()&& parent->rightNode() != NULL){

node = parent->rightNode();while (node->leftNode() != NULL|| node->rightNode() != NULL){

stack.push(node);if (node->leftNode() != NULL)

node = node->leftNode();else

node = node->rightNode();}

}else{

stack.pop();node = parent;

}}return *this;

Outline

2 List Traversals

3 Reverse Iterators

5 Assignment

Assignment

AssignmentRead Section 14.6.Create a LevelorderIterator class for binary trees.

List and Binary Tree Iterator...

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