Linked List Improvements& Memory

BigO's

• What is BigO for our basic linked list operations?

InsertStart Insert at middle

InsertEnd Retrieve First Value

Retrieve Middle Value

Remove From End

Remove From

Beginning

Get Length

BigO's

• What is BigO for our basic linked list operations?

InsertStart Insert at middle

InsertEnd Retrieve First Value

Retrieve Middle Value

Remove From End

Remove From

Beginning

Get Length

O(1) O(n) O(n) O(1) O(n) O(n) O(1) O(n)

Linked List Gripes

• Issues with basic linked list:– No easy way to get length– No easy way to put something at the end

Length

• Keep track of length of list– Increment on any insert– Decrement on removal

• listSize() now O(1)

Length Side Benefit

• Cheap list size can simplify other algorithms– Error check early

InsertEnd

• Want to efficiently implement:InsertEnd(int value)

• What do we need?

Tail Pointer

• Tail pointer– Always points to last element

InsertEndInsertEnd(value)Node* newNode = new Node(value)tail->next = newNodetail = newNodelength++

InsertEndInsertEnd(value)Node* newNode = new Node(value)tail->next = newNodetail = newNodelength++

InsertEndInsertEnd(value)Node* newNode = new Node(value)tail->next = newNodetail = newNodelength++

InsertEndInsertEnd(value)Node* newNode = new Node(value)tail->next = newNodetail = newNodelength++

InsertEnd• Special case : insertEnd on empty list– Pass off to insertStart

InsertEnd(value)If length == 0

insertStart(value)return

Node* newNode = new Node(value)tail->next = newNodetail = newNodelength++

Tail Issues

• InsertEnd(value) now O(1)

• But need to worry about tail in other situations– InsertStart on empty list – InsertAt on last node– RemoveAt on last node

Tail Issues

• Example:insertStart on empty list

Tail Issues

• ExampleRemoving at current tail

removeAt(2) calledFound current and nodeToRemove

Tail Issues

• ExampleRemoving at current tail

removeAt(2) calledRemoved node from list

Tail Issues

• ExampleRemoving at current tail

removeAt(2) calledDeleted from memory

Tail Issues

• ExampleRemoving at current tail

removeAt(2) calledWe have a new tail!

Memory Management

• Destructor needs to free allocated nodes– Must delete each individually

Destruct~LinkedList()Node* temp = headwhile head is not null

head = head->nextdelete temptemp = head

Destruct~LinkedList()Node* temp = headwhile head is not null

head = head->nextdelete temptemp = head

Destruct~LinkedList()Node* temp = headwhile head is not null

head = head->nextdelete temptemp = head

Destruct~LinkedList()Node* temp = headwhile head is not null

head = head->nextdelete temptemp = head

Destruct Alternative

• Destructor made simple:

~LinkedList()while head is not null

removeFirst

Copy Constructor• Want a deep copy– Whole new list of nodes with identical data, in same order– Length, head and tail set correctly

foreach node in otherget node's valueinsert value at end

Copy Constructor• Want a deep copy– Whole new list of nodes with identical data, in same order– Length, head and tail set correctly

foreach node in otherget node's valueinsert value at end

Copy Constructor• Want a deep copy– Whole new list of nodes with identical data, in same order– Length, head and tail set correctly

foreach node in otherget node's valueinsert value at end

Copy Constructor• Want a deep copy– Whole new list of nodes with identical data, in same order– Length, head and tail set correctly

foreach node in otherget node's valueinsert value at end

Copy Constructor• Want a deep copy– Whole new list of nodes with identical data, in same order– Length, head and tail set correctly

foreach node in otherget node's valueinsert value at end

…

Assignment Operator• myList = other

– Delete nodes 4 and 5– Copy nodes from other