Generally a Linked List means "Singly Linked List". It is a chain of records known as Nodes. Each node has at least two members, one of which points to the next Node in the list and the other holds the data.

Figure 1: Singly Linked List |

struct Node { int Data; struct Node *Next; };Variable Data holds the data in the Node (It can be a pointer variable pointing to the dynamically allocated memory) while Next holds the address to the next Node in the list.

Figure 2: Node in a Singly Linked List |

Basic Operations on a Singly Linked List

- Traversing a List
- Inserting a Node in the List
- Deleting a Node from the List

**Traversing a Singly Linked List**

Traversing a Singly Linked List is the basic operation we should know before we do other operations like Inserting a Node or Deletion of a Node from the Singly Linked List. Let us see how to traverse Singly Linked List in Figure 1.Let us assume

**Head**points to the first Node in the List.

**Pseudocode**:

cur = head forever: if cur == NULL break cur = cur->Next

**Complexity:**

To traverse a complete list of size 'n' it takes

- Time complexity:
**O(n)**. - Space Complexity:
**O(1)**for storing one temporary variable.

**Inserting a Node in Singly Linked List**

There are 3 possible cases for inserting a Node in a Singly Linked List.

**Inserting a Node at the beginning of the List**

In this case**newNode**is inserted at the starting of the List. We have to update**Next**in**newNode**to point to the previous**firstNode**and also update**Head**to point to**newNode**.

**Pseudocode**:

firstNode = Head->Next newNode->Next = firstNode Head->Next = newNode

But above pseudocode can be modified to reduce the space complexity by removing the temporary variable usage as shown below

newNode->Next = Head->Next Head->Next = newNode

**Complexity**:

Time Complexity: O(1)

Space Complexity: None

**Sourcecode**:void addBeg(int num) { struct Node *temp; temp=(struct Node *)malloc(sizeof(struct Node)); temp->Data = num; if (Head == NULL) { //List is Empty Head=temp; Head->Next=NULL; } else { temp->Next=Head; Head=temp; } }

**Inserting a Node at the End of the List**

In order to add the node at the end of the list we have to first traverse to the end of the List. Then we have to update the**Next**variable in**lastNode**pointing to**newNode**.

**Pseudocode**:cur = head forever: if cur->Next == NULL break cur->Next = newNode

**Complexity**:

To add a Node at the end of a list whose length is 'n'

Time Complexity: O(n)

Space Complexity: O(1)

**Sourcecode**:

void addEnd(int num) { struct Node *temp1, *temp2; temp1=(struct Node *)malloc(sizeof(struct Node)); temp1->Data=num; // Copying the Head location into another node. temp2=Head; if(Head == NULL) { // If List is empty we create First Node. Head=temp1; Head->Next=NULL; } else { // Traverse down to end of the list. while(temp2->Next != NULL) temp2=temp2->Next; // Append at the end of the list. temp1->Next=NULL; temp2->Next=temp1; } }

**Inserting a Node at position 'p' in the List**

To add at the position 'p' we have to traverse the list until we reach the position 'p'. For this case have to maintain two pointers namely**prevNode**and**curNode**. Since Singly Linked Lists are uni-directional we have to maintain the information about previous Node in**prevNode**. Once we reach the position 'p' we have to modify**prevNode****Next**pointing to**newNode**while**newNode**points to**curNode**.

**Pseudocode**:

curNode = head curPos = 1 forever: if curPos == P || curNode == NULL break prevNode = curNode curNode = curNode->Next curPos++ if curNode != NULL: prevNode->Next = newNode newNode->Next = curNode

**Complexity**:

Time Complexity: O(n) in worst case.

Space Complexity: O(3)

**Sourcecode**:void addAt(int num, int loc) { int i; struct Node *temp, *prev_ptr, *cur_ptr; cur_ptr=Head; if(loc > (length()+1) || loc <= 0) { printf("\nInsertion at given location is not possible\n "); } else { // If the location is starting of the list if (loc == 1) { addBeg(num); } else { for(i=1;i<loc;i++) { prev_ptr=cur_ptr; cur_ptr=cur_ptr->Next; } temp=(struct Node *)malloc(sizeof(struct Node)); temp->Data=num; prev_ptr->Next=temp; temp->Next=cur_ptr; } } } // Counting number of elements in the List int length() { struct Node *cur_ptr; int count=0; cur_ptr=Head; while(cur_ptr != NULL) { cur_ptr=cur_ptr->Next; count++; } return(count); }

**Next Article**: Deleting a Node from a Singly Linked List

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but

while deleting a node from list based on data

it will return the control when it reaches the 1st node (node.data==num) but the list contains the duplication of data,How it is going to delete the next node..

Plz provide the solution...

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temp2=temp1;

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if (Head == NULL)

ReplyDelete{

//List is Empty

Head=temp;

Head->Next=NULL;

}

else

{

temp->Next=Head;

Head=temp;

}

actually, you don't need the special case Head==NULL. we can simply make Head point to the new node and set node->next to whatever Head was pointing to, and if it was NULL then we'll just have initialized the new node's Next member which we must do anyway.

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if (Head == NULL)

{

//List is Empty

Head=temp;

temp->Next=NULL;

}

@preetham

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