# Swap elements of adjacent nods of the Linked List

“** Swap elements of adjacent nods of the Linked List**” is one of the basic problem of the Linked List. Here, we are given a linked list and our task is to swap elements of adjacent nodes of a linked list.

**Example:**

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

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

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

**C++ Program to pairwise swap elements of a linked list is as follows:**

/* C++ Program to pairwise swap elements of a 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 */ void insert_end(Node **head, int ele) { /* 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 */ if(*head == NULL) { *head = new_node; 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; temp = (*head); while(temp->next != NULL) temp=temp->next; temp->next = new_node; } /* Function to pairwise swap elements of a linked list */ void swapAdjacent(Node *head) { /* If Linked List is empty or contains only one node, then return. */ if(head == NULL || head->next == NULL) 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. */ Node *temp = head; 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 */ void print(Node *head) { Node *temp = head; while(temp!=NULL) { cout<<temp->data<<" "; temp=temp->next; } cout<<endl; } int main() { Node *head = NULL; /* Inserting Some Nodes in the Linked List */ insert_end(&head,12); insert_end(&head,34); insert_end(&head,88); insert_end(&head,56); insert_end(&head,66); insert_end(&head,78); cout<<"Printing the Linked List before Swapping:\n"; print(head); /* swap adjacent node data */ swapAdjacent(head); cout<<"\nPrinting the Linked List after Swapping:\n"; print(head); }

Printing the Linked List before Swapping: 12 34 88 56 66 78 Printing the Linked List after Swapping: 34 12 56 88 78 66OUTPUT:

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