Chapter 17Linked List

Saurav KarmakarSpring 2007

LISTS Easiest implementation of LIST --- ARRAY

:: has Disadvantages.

1) To insert an item at the beginning or middle of an array sliding lots of items over one place to

make room :: ~ O(n)

2) Arrays have a fixed length :: can't be changed.

Adding items to a list Allocation a whole new array if the array containing LIST is full and then move all the items from the old array to the new one.

Linked List Consists of connected, dynamically

allocated nodes.

A linked list is made up of "nodes". Each node has two components: an item, and a reference to the next node in the list.

Comparison with Array1. Arrays

contiguousdirect access of elementsinsertion / deletion difficult

2. Linked Listsnoncontiguousmust scan for elementinsertion /deletion easy

1. Arrayscontiguousdirect access of elementsinsertion / deletion difficult

2. Linked Listsnoncontiguousmust scan for elementinsertion /deletion easy

arrayname

for (int i = 0; i < length; i++) cout<< a[i];

for (ListNode p = theList.first; p != null; p = p.next) cout<< p.data ;

for (int i = 0; i < length; i++) cout<< a[i];

for (ListNode p = theList.first; p != null; p = p.next) cout<< p.data ;

a

Iterating through the data structureIterating through the data structure

class ListNode{ Object data; ListNode* next;}

At any point, we can add a new last item x by doing this: Last->next = new ListNode();last = last->next;Last->data = x;Last->next = null;

A0 A1 A2

first last

Adding an element

class ListNode{ Object data; ListNode* next;}

At any point, we can add a new last item x by doing this: Last->next = new ListNode();last = last->next;Last->data = x;Last->next = null;

A0 A1 A2

first last

class ListNode{ Object data; ListNode* next;}

At any point, we can add a new last item x by doing this: last->next = new ListNode();last = last->next;Last->data = x;Last->next = null;

A0 A1 A2

first last

class ListNode{ Object data; ListNode* next;}

At any point, we can add a new last item x by doing this: last->next = new ListNode();last = last->next;Last->data = x;Last->next = null;

A0 A1 A2 x

first last

class ListNode{ Object data; ListNode* next;}

At any point, we can add a new last item x by doing this: Last->next = new ListNode();last = last->next;Last->data = x;Last->next = null;

A0 A1 A2 x

first last

class ListNode{ Object element; ListNode* next;}At any point, we can insert a new item x by doing this:tmp = new ListNode();Tmp->element = x;Tmp->next = current->next;Current->next = tmp;

last

Inserting an element

A0 A1 A2

first current

class ListNode{ Object element; ListNode* next;}At any point, we can insert a new item x by doing this:

tmp = new ListNode();Tmp->element = x;Tmp->next = current->next;Current->next = tmp;

Inserting an element

A0 A1 A2

first lastcurrent

tmp

class ListNode{ Object element; ListNode* next;}At any point, we can insert a new item x by doing this:

tmp = new ListNode();Tmp->element = x;Tmp->next = current->next;Current->next = tmp;

Inserting an element

A0 A1 A2

first lastcurrent x

tmp

class ListNode{ Object element; ListNode* next;}At any point, we can add a new last item x by doing this: tmp = new ListNode();Tmp->element = x;Tmp->next = current->next;current->next = tmp;

Inserting an element

A0 A1 A2

first lastcurrent x

tmp

class ListNode{ Object element; ListNode* next;}At any point, we can add a new last item x by doing this: tmp = new ListNode();Tmp->element = x;Tmp->next = current->next;Current->next = tmp;

Inserting an element

A0 A1 A2

first lastcurrent x

tmp

Simplified version

Current->next = new ListNode(x, current->next)

tmp = new ListNode();

Current->next = tmp;

Tmp->next = current->next;

Tmp->element = x;

class ListNode{ Object element; ListNode* next;}

Current->next = current->next->next;

Deleting an element

A0 A1 A2

current last

class ListNode{ Object element; ListNode* next;}

Current->next = current->next->next; Memory leak!

Deleting an element

A0 A1 A2

lastcurrent

Delete a Node

Node *deletedNode = current->next;

Current->next = current->next->next;

Delete deletedNode;

Length Function The Length function takes a linked list and

computes the number of elements in the list.

/*Given a linked list head pointer, compute and return the number of nodes in the list.*/

int Length(struct node* head) {struct node* current = head;int count = 0;while (current != NULL) {count++;current = current->next;}return count;}

a b c

header

Header nodes allow us to avoid special cases [in the code] such as insertion of the first element and removal of the last element.

The header node holds no data but serves to satisfy the requirement that every node have a previous node.

Not necessarily a standard implementation.

Header node

a b c

head tail

class DoubleListNode{ Object element; ListNode* next; ListNode* prev;}

class DoubleListNode{ Object element; ListNode* next; ListNode* prev;}

A doubly linked list allows bidirectional traversal by storing two pointers per node.

Doubly Linked Lists

head tail// constructorDoubleList(){ head = new DoubleListNode (); tail = new DoubleListNode (); head->next = tail; tail->prev = head;}

Empty Doubly Linked List

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

Inserting into a Doubly Linked List

a c

head tailcurrent

Inserting into a Doubly Linked List

a c

head tail

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

bcurrent

Inserting into a Doubly Linked List

a c

head tail

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

bcurrent

Inserting into a Doubly Linked List

a c

head tail

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

bcurrent

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

Inserting into a Doubly Linked List

a c

head tailbcurrent

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

Inserting into a Doubly Linked List

a c

head tailbcurrent

newNode = new DoublyLinkedListNode()newNode->prev = current;newNode->next = current->next;newNode->prev->next = newNode;newNode->next->prev = newNode;current = newNode

Inserting into a Doubly Linked List

a c

head tailbcurrent

Circular Linked Lists

a b c d

first

Sorted Linked List

A sorted link list is one in which items are in sorted order.

The major difference from linked list is the insertion operation.