17 linkedlist (1)
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Linked List
CSE102 – Programming Fundamentals
Array Implementation
Elements are stored in contiguous array positions
Array Implementation...
Requires an estimate of the maximum size of the list waste space
Print all element and find an specific number: Linear – Traverse whole array
Print i’th Element: Constant time - (Example: printf(“%d”,a[i]);
insert and delete: slow e.g. insert at position 0 (making a new element)
requires first pushing the entire array down one spot to make room
e.g. delete at position 0 requires shifting all the elements in the list up one
Pointer Implementation (Linked List)
Ensure that the list is not stored contiguously use a linked list a series of structures that are not necessarily adjacent in
memory
Each node contains the element and a pointer to a structure containing its successor
the last cell’s next link points to NULL Compared to the array implementation,
the pointer implementation uses only as much space as is needed for the elements currently on the listbut requires space for the pointers in each cell
Nodes and Linked Lists
A linked list is a list that can grow and shrink while the program is running
A linked list is constructed using pointers A linked list often consists of structs that
contain a pointer variable connecting them to otherdynamic variables
A linked list can be visualized as items, drawn asboxes, connected to other items by arrows
10 12 14 endhead
Linked Lists
A linked list is a series of connected nodesEach node contains at least
A piece of data (any type) Pointer to the next node in the list
Head: pointer to the first nodeThe last node points to NULL
10
Head
20 30
10
data pointer
node
Implementing Nodes
Nodes are implemented in C as “struct” Example: A structure to store two data items and
a pointer to another node of the same type, along with a type definition might be:
struct Node { int item; struct Node *next; };
Self-Referential Structures
A structure may not contain an object of its own type.
struct Node { int item; struct Node n; /* Invalid */ };
However, a structure may contain a pointer to the same type.
struct Node { int item; struct Node *pn; /* Valid */ };
The head of a List
The box labeled head, is not a node, but a pointer variable that points to a node.
Pointer variable head is declared as:
struct Node *head;
10
head
20 30
Accessing Items in a Node
One way to change the number in the first node from 10 to 12: head->item = 12;
12
head
20 30
NULL
The defined constant NULL is used as… An end marker for a linked list
A program can step through a list of nodes by followingthe pointers, but when it finds a node containing NULL, it knows it has come to the end of the list
The value of a pointer that has nothing to point toThe value of NULL is 0Any pointer can be assigned the value NULL:
double* there = NULL;
Linked Lists
A linked list is a list of nodes in which each node has a member variable that is a pointer that points to the next node in the list The first node is called the head The pointer variable head, points to the first node
The pointer named head is not the head of the list…it points to the head of the list
The last node contains a pointer set to NULL
Building a Linked List:Declaring Pointer Variable head
With the node defined and a type definition to
make or code easier to understand, we can declare the pointer variable head:
struct Node *head; head is a pointer variable that will point to the head
node when the node is created
Building a Linked List:Creating the First Node
To create the first node, the operator new is usedto create a new dynamic variable:
head = (struct Node *)malloc(sizeof(struct Node));
Now head points to the first, and only, node in the list
Building a Linked List:Initializing the Node
Now that head points to a node, we need to give values to the member variables of the node:
head->item = 10; head->next = NULL; Since this node is the last node, the link is set to
NULL10
head
Traversing Singly Linked List
void Traverse(struct Node *head) Print the data of all the elements Print the number of the nodes in the list From “main()” function call “Traverse(head)”.
void Traverse(struct Node *head){ int num = 0; struct Node *currNode; currNode = head; while (currNode != NULL){
printf(“%d “,currNode->item);currNode = currNode->next;num++;
} printf("Number of nodes in the list: %d\n”,num);}
Traversing Singly Linked List (2)
Output: 12 currnode = headNum: 1
12
head
20 30
currnode
Traversing Singly Linked List (2)
Output: 12 20Num: 2
currnode = currnode->next
12
head
20 30
currnode
Traversing Singly Linked List (2)
Output: 12 20 30Num: 3
currnode = currnode->next
12
head
20 30
currnode
Traversing Singly Linked List (2)
Output: 12 20 30Num: 3
currnode = NULL at this moment. So function terminates.
12
head
20 30
currnode
Inserting a new node
Node* InsertNode(int index, double x) Insert a node with data equal to x after the index’th elements.
(i.e., when index = 0, insert the node as the first element; when index = 1, insert the node after the first element, and
so on) If the insertion is successful, return the inserted node. Otherwise, return NULL. (If index is < 0 or > length of the list, the insertion will fail.)
Steps Locate index’th element Allocate memory for the new node Point the new node to its successor Point the new node’s predecessor to the new node
newNode
index’th element
Inserting a new node
Possible cases of InsertNode Insert into an empty list Insert in front Insert at back Insert in middle
But, in fact, only need to handle two cases Insert as the first node (Case 1 and Case 2) Insert in the middle or at the end of the list (Case 3
and Case 4)
Inserting a new node
struct Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;struct Node* currNode = head;while (currNode!=NULL && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = (struct Node *)malloc(sizeof(struct Node));newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Try to locate index’th node. If it doesn’t exist, return NULL.
Inserting a new node
struct Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;struct Node* currNode = head;while (currNode!=NULL && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = (struct Node *)malloc(sizeof(struct Node));newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Create a new node
Inserting a new node
struct Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;struct Node* currNode = head;while (currNode!=NULL && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = (struct Node *)malloc(sizeof(struct Node));newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Insert as first elementhead
newNode
Inserting a new node
struct Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;struct Node* currNode = head;while (currNode!=NULL && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = (struct Node *)malloc(sizeof(struct Node));newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Insert after currNode
newNode
currNode
Finding a node
int FindNode(double x, struct Node *head) Search for a node with the value equal to x in the list. If such a node is found, return its position. Otherwise,
return 0.
int FindNode(double x, struct Node *head) {struct Node* currNode = head;int currIndex = 1;while (currNode!=NULL && currNode->data != x) {
currNode = currNode->next;currIndex++;
}if (currNode!=NULL) return currIndex;else return 0;
}
Deleting a node
int DeleteNode(double x) Delete a node with the value equal to x from the list. If such a node is found, return its position. Otherwise,
return 0.Steps
Find the desirable node (similar to FindNode) Release the memory occupied by the found node Set the pointer of the predecessor of the found node to the
successor of the found nodeLike InsertNode, there are two special cases
Delete first node Delete the node in middle or at the end of the list
Deleting a node
int DeleteNode(double x) {struct Node* prevNode = NULL;struct Node* currNode = head;int currIndex = 1;while (currNode!=NULL && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode!=NULL) {
if (prevNode) {prevNode->next = currNode->next;delete currNode;
}else {
head = currNode->next;delete currNode;
}return currIndex;
}return 0;
}
Try to find the node with its value equal to x
Deleting a node
int DeleteNode(double x) {struct Node* prevNode = NULL;struct Node* currNode = head;int currIndex = 1;while (currNode!=NULL && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode!=NULL) {
if (prevNode!=NULL) {prevNode->next = currNode->next;free (currNode);
}else {
head = currNode->next;delete currNode;
}return currIndex;
}return 0;
}
currNodeprevNode
Deleting a node
int DeleteNode(double x) {struct Node* prevNode = NULL;struct Node* currNode = head;int currIndex = 1;while (currNode!=NULL && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode!=NULL) {
if (prevNode!=NULL) {prevNode->next = currNode->next;free (currNode);
}else {
head = currNode->next;free( currNode);
}return currIndex;
}return 0;
}
currNodehead
Destroying the list
void DeleteList(struct Node *head) Use the DeleteList() function to release all the
memory used by the list. Step through the list and delete each node one by one.
void DelteList(struct Node *head) { struct Node* currNode = head, *nextNode = NULL; while (currNode != NULL) {
nextNode = currNode->next;// destroy the current nodefree (currNode);currNode = nextNode;
}}
Linked List (Other Operaions)
Find the highest and lowest element from a linked list.
Sort the linked listInsert a node before (and after) a given number of a
linked listReverse the linked listPrint the linked list in reverse order (using (and
without using)recursion)Delete the last element of a linked list (where you
are given the head of the linked list only)Find the middle element of a linked list.