Swap elements of adjacent nodes of the Linked List” is one of the basic programming problem based on Linked List data structure. Here, we are given a linked list and our task is to swap elements of adjacent nodes of the linked list.

Example:

```Suppose, we need to swap elements of adjacent nodes of the following linked list:
12 -> 13 -> 15 -> 21 -> 67
After swapping:
13 -> 12 -> 21 -> 15 -> 67
Other example:
12 -> 13 -> 15 -> 21
After swapping:
13 -> 12 -> 21 -> 15 ```

The steps required to swap elements of adjacent nodes of the linked list is as follows:

1. If linked list is empty or contains only one node, then return.
2. Traverse the linked list and swap each node’s data with the next node’s data, if exist.
3. Increment the pointer by two nodes while traversing.

#### C++ Program to swap elements of adjacent nodes of the linked list is as follows:

```/* C++ Program to swap elements of adjacent nodes of the linked list */
#include<bits/stdc++.h>
using namespace std;

/* Strcuture of the Node of the Linked List */
typedef struct node
{
int data;
struct node *next;
}Node;

/* Function to Insert Node at the end of the Linked List */
{
/* Creating a new node */
Node *new_node;
new_node = (struct node*)malloc(sizeof(struct node));
new_node->data = ele;
new_node->next = NULL;

/* check whether the linked list is empty or not */

/* If Linked List is Empty, then new node will become head of the linked list */
{
return;
}

/* If Linked List is not Empty, then traverse the complete linked list and point
the pointer of last node of the linked list to the new node of the linked list */
Node *temp = NULL;
while(temp->next != NULL)
temp=temp->next;
temp->next = new_node;
}

/* Function to pairwise swap elements of a linked list */
{
/* If Linked List is empty or contains only one node, then return. */
return;

/* If Linked List contains more than one nodes, then traverse the
linked list and swap each node’s data with the next node’s data, if exist.
*/
while(temp && temp->next)
{
int temp_var = temp->data;
temp->data = temp->next->data;
temp->next->data = temp_var;

temp = temp -> next -> next;
}
}

/* Function to Print the Linked List */
{
while(temp!=NULL)
{
cout<<temp->data<<" ";
temp=temp->next;
}
cout<<endl;
}
int main()
{
/* Inserting Some Nodes in the Linked List */
cout<<"Printing the Linked List before Swapping:\n";

/* swap adjacent node data */

cout<<"\nPrinting the Linked List after Swapping:\n";
```OUTPUT: