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Doubly Linked Lists
CS 308 – Data Structures

Node data
• info: the user's data
• next, back: the address of the next and
previous node in the list
.back .next
.info

Node data (cont.)
template<class ItemType>
struct NodeType {
ItemType info;
NodeType<ItemType>* next;
NodeType<ItemType>* back;
};

Finding a List Item
• We no longer need to use prevLocation (we can
get the predecessor of a node using its back
member)

Inserting into a Doubly Linked List
1. newNode->back = location->back; 3. location->back->next=newNode;
2. newNode->next = location 4. location->back = newNode;

FindItem(listData, item, location, found)
• RetrieveItem, InsertItem, and DeleteItem all
require a search !
• Write a general non-member function FindItem
that takes item as a parameter and returns location
and found.
• InsertItem and DeleteItem need location (ignore
found)
• RetrieveItem needs found (ignores location)

Finding a List Item (cont.)
void FindItem(NodeType<ItemType>* listData, ItemType item,
NodeType<ItemType>* &location, bool &found)
{
// precondition: list is not empty
bool moreToSearch = true;
location = listData;
found = false;
while( moreToSearch && !found) {
if(item < location->info)
moreToSearch = false;
else if(item == location->info)
found = true;
else {
if(location->next == NULL)
moreToSearch = false;
else
location = location->next;
}
}
}

How can we distinguish between the
following two cases?

Special case: inserting in the beginning

void SortedType<ItemType>::InsertItem(ItemType item)
{
NodeType<ItemType>* newNode;
NodeType<ItemType>* location;
bool found;
newNode = new NodeType<ItemType>;
newNode->info = item;
if (listData != NULL) {
FindItem(listData, item, location, found);
if (location->info > item) {
newNode->back = location->back;
newNode->next = location;
if (location != listData) // special case
(location->back)->next = newNode;
else
listData = newNode;
location->back = newNode;
}
(1)
(2)
(3)
(4)
(3)

(cont.)
else { // insert at the end
newNode->back = location;
location->next = newNode;
newNode->next = NULL;
}
}
else { // insert into an empty list
listData = newNode;
newNode->next = NULL;
newNode->back = NULL;
}
length++;
}

Deleting from a Doubly Linked List
• Be careful about the end cases!!

Headers and Trailers
• Special cases arise when we are dealing
with the first or last nodes
• How can we simplify the implementation?
– Idea: make sure that we never insert or delete
the ends of the list
– How? Set up dummy nodes with values outside
of the range of possible values

Headers and Trailers (cont.)
• Header Node: contains a value smaller than
any possible list element
• Trailer Node: contains a value larger than
any possible list element

A linked list as
an array of records
• What are the advantages of using linked
lists?
(1) Dynamic memory allocation
(2) Efficient insertion-deletion (for sorted lists)
• Can we implement a linked list without
dynamic memory allocation ?

A linked list
as an array
of records
(cont.)

Case Study: Implementing a
large integer ADT
• The range of integer values varies from one
computer to another
• For long integers, the range is
[-2,147,483,648 to 2,147,483,647]
• How can we manipulate larger integers?

Case Study: Implementing a large
integer ADT (cont.)
- A special list ADT

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LinkedDoublyLists.ppt

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