Chapter 17 Linked List

Chapter 17Linked List Bernard Chen Spring 2006

Arrays • contiguous • direct access of elements • insertion / deletion difficult • Linked Lists • noncontiguous • must scan for element • insertion /deletion easy arrayname Comparison with array

Iterating through a data structure a for (int i = 0; i < length; i++) cout<< a[i]; for (ListNode p = theList.first; p != null; p = p.next) cout<< p.data ;

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 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 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 current first Inserting an element last 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;

A0 A1 A2 current first last tmp Inserting an element 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;

A0 A1 A2 current x first last tmp Inserting an element 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;

A0 A1 A2 current x first last tmp Inserting an element 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;

A0 A1 A2 current x first last tmp Inserting an element 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;

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

A0 A1 A2 current last Deleting an element class ListNode { Object element; ListNode* next; } Current->next = current->next->next;

A0 A1 A2 current last Deleting an element class ListNode { Object element; ListNode* next; } Current->next = current->next->next; Memory leak!

Delete a Node Node *deletedNode = current->next; Current->next = current->next->next; Delete deletedNode;

Header node 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.

a b c head tail Doubly Linked Lists A doubly linked list allows bidirectional traversal by storing two pointers per node. class DoubleListNode { Object element; ListNode* next; ListNode* prev; }

head tail Empty Doubly Linked List // constructor DoubleList() { head = new DoubleListNode (); tail = new DoubleListNode (); head->next = tail; tail->prev = head; }

a c head tail current Inserting into a 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 b head tail current 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 current b head tail 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 b head tail current newNode = new DoublyLinkedListNode() newNode->prev = current; newNode->next = current->next; newNode->prev->next = newNode; newNode->next->prev = newNode; current = newNode

Circular Linked Lists a b c d first

Sorted Linked List • A sorted link list is one in which items are in sorted order. It can be derived from a list class. • The major difference from linked list is the insertion operation.

In Class exercise • Suppose you have a pointer to a node in a single linked list that is guaranteed not to be the last node in the list. You don’t have pointers to any other nodes. Describe an O(1) algorithm that logically removes the value stored in such a node from the linked list, maintaining the integrity of the linked list.

Chapter 17 Linked List