List Data Type (4.1, 4.6, 4.9)


















What's a List?


	1. a container that holds objects
	2. each object has an index or position
	3. objects are kept in the order given by the user

















What operations are supported by a List?
What's the abstract interface for a List?


	size();
	append(item);
	remove(index);
	insert(index, item);
	get(index);
	set(index, item);



What happens to the item at index 2 when the item at index 1 is removed?

What happens to the item at index 2 when an item is inserted at index 2?



















Classwork
You may work with a partner.

What does the program print?

	List L1;
	L1.append(1);
	L1.append(2);
	L1.append(4);
	print(L1);

	List L2;
	for (int i = 0; i < L1.size(); i++)
	    L2.insert(0, L1.get(i));
	print(L2);

	for (int i = 0; i < L1.size(); i++)
	    L2.insert(2*i, L1.get(i));
	print(L2);

	for (int i = 0; i < L1.size(); i++)
	    L2.set(i, L1.get(i));
	print(L2);

	for (int i = 0; i < L2.size(); i++)
	    L2.remove(i);
	print(L2);

















Lists in the C++ Library


	#include <vector>

	std::vector


	#include <list>

	std::list

















What are some of the operations supported by std::vector?


	size_t size() const;
	void push_back ( const ItemType& item );
	iterator erase ( iterator index );
	iterator insert ( iterator index, const ItemType& item );
	ItemType& at ( int index );
	ItemType& operator[] ( int index );


DEMO	(write reverse method using indexes)
















What are some of the operations supported by std::list?


	size_t size() const;
	void push_back ( const ItemType& item );
	iterator erase ( iterator index );
	iterator insert ( iterator index, const ItemType& item );


DEMO	(change vector to list)

















Iterators


How do you iterate over an array?


	for (int i = 0; i < length; i++)
	    print(array[i]);


How do you iterate over a list?
Why do you need an Iterator?
Why can't you use indexing?


	some containers don't support indexing
	internal structure can't be indexed efficiently




















What's an Iterator?


	a pointer that steps through the objects in a container


What operations are supported by an Iterator?
What's the abstract interface for an Iterator?


	create();
	access();
	increment();
	compare();


















How do you create and use an Iterator on a list?


	list<int> items;

	list<int>::iterator i = items.begin();

	while (i != items.end()) {
	    cout << *i;
	    i++;
	}


DEMO	(rewrite reverse using iterators)

















Why List?


A 'vector' can do most anything a 'list' can do.
A 'list' cannot do indexing, while a 'vector' can.
Why is a 'list' useful?


DEMO	(time for insert on vector vs list)