The List ADT & Array Lists

The List ADT & Array Lists Joe Meehean

List ADT Item 0 Item 1 Item 2 … Item N • Ordered collection of items • not necessarily sorted • 0-index (first item is item 0) • Abstraction

List ADT • Expected operations • add to end (append) • insert at position X • membership (does it contain…) • size • is empty? • get item at position X • remove item at position X

List ADT 0 1 2 3 0 1 2 3 4 Insert Zat 2 A B C D A B Z C D • Cannot insert past end of list • e.g., insert X at 6 • Can insert at the end • e.g., insert X at 5 • Insert in detail • shifts all items at positions greater than the insert position to the right

List ADT 0 1 2 3 0 1 2 Remove at 1 A B C D A C D • Remove in detail • removes an item at position Y • shifts items after Y left

Lists vs Arrays • Similarities • ordered collections of objects • indexed at 0 • Differences • lists can grow or shrink • don’t need to know data size in advance • size is always number of items, not capacity • lists can’t add elements at arbitrary position • no inserts past end • can insert anywhere in array

Array List • List Implementations • internal view (how data is stored and managed) • array list • linked lists

Array List • Array List • list implementation using an array • implementation hidden in a C++ class • data stored in an array • stores a counter of number of elements • Wrap list functionality around an array • Special Cases • out of bounds: insert, add, get, remove • array is full: insert and add

Array List • Out of bounds • index outside of range of list • throw an exception • OR return garbage (very C++) • Array is full • allocate a bigger array • copy old data to new array • insert new item

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); 0 1 2 3 4 data 5 11 17 4 size: 4 capacity: 5

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); 0 1 2 3 4 data 5 11 17 4 45 size: 4 5 capacity: 5

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); 0 1 2 3 4 data 5 11 17 4 45 size: 5 capacity: 5

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); 9 8 7 6 0 1 2 3 4 5 tmp 0 1 2 3 4 data 5 11 17 4 45 size: 5 capacity: 5

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); 9 8 7 6 0 1 2 3 4 5 tmp 5 11 17 4 45 0 1 2 3 4 data 5 11 17 4 45 size: 5 capacity: 5

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); 9 8 7 6 0 1 2 3 4 5 tmp 5 11 17 4 45 0 1 2 3 4 data 5 11 17 4 45 size: 5 capacity: 5 10

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); 9 8 7 6 0 1 2 3 4 5 5 11 32 17 4 45 data size: 5 6 capacity: 10

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); list.removeAtIndex(3); 9 8 7 6 0 1 2 3 4 5 5 11 32 17 4 45 data size: 6 capacity: 10

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); list.removeAtIndex(3); 9 8 7 6 0 1 2 3 4 5 5 11 32 17 4 45 data size: 6 5 capacity: 10

Array List ArrayList list; // insert a bunch of stuff ... list.add(45); list.add(32); list.removeAtIndex(3); 9 8 7 6 0 1 2 3 4 5 5 45 17 4 32 data size: 6 5 capacity: 10

Questions?

Array List Algorithm Analysis • Get size • O(1) • Get the Mth item (e.g., data[M]) • O(1) • Clear the list • O(1)

Array List Algorithm Analysis • Add at the end • avg case: O(1) • worst case: O(N) • Add to the front • O(N) • Remove at the end • O(1) • Remove at the front • O(N)

Lists in C++ • Standard Template Library (STL) • provides many data structures for C++ • including lists • Array List is implemented by STL’s vector • vector is a template class • vector<T> • e.g., vector<int> intList;

vector<T> • int size() const • returns the number of elements stored • void clear() • removes all elements from vector • void push_back(const T& t) • adds t to the end of the list • void pop_back() • removes the last item from the list

vector<T> • T& operator[](intidx) • returns a reference to the object at index • gives mutable access to this object • e.g., given vector vv[5] = 15; // 6th element is now 15v[5]++; // 6th element is now 16 • provides no bound checking • Can also remove items using Iterators • coming soon

Questions?

The List ADT & Array Lists