pairwise_swap_nodes.cpp

// C++ program to pairwise swap elements
// in a given linked list
#include <bits/stdc++.h>
using namespace std;

/* A linked list node */
class Node {
public:
	int data;
	Node* next;
};

/* Function to pairwise swap elements
of a linked list */
void pairWiseSwap(Node* head)
{
	Node* temp = head;

	/* Traverse further only if
	there are at-least two nodes left */
	while (temp != NULL && temp->next != NULL) {
		/* Swap data of node with
		its next node's data */
		swap(temp->data,
			temp->next->data);

		/* Move temp by 2 for the next pair */
		temp = temp->next->next;
	}
}

/* Function to add a node at the
beginning of Linked List */
void push(Node** head_ref, int new_data)
{
	/* allocate node */
	Node* new_node = new Node();

	/* put in the data */
	new_node->data = new_data;

	/* link the old list off the new node */
	new_node->next = (*head_ref);

	/* move the head to point
	to the new node */
	(*head_ref) = new_node;
}

/* Function to print nodes
in a given linked list */
void printList(Node* node)
{
	while (node != NULL) {
		cout << node->data << " ";
		node = node->next;
	}
}

// Driver Code
int main()
{
	Node* start = NULL;

	/* The constructed linked list is:
	1->2->3->4->5 */
	push(&start, 5);
	push(&start, 4);
	push(&start, 3);
	push(&start, 2);
	push(&start, 1);

	cout << "Linked list "
		<< "before calling pairWiseSwap()\n";
	printList(start);

	pairWiseSwap(start);

	cout << "\nLinked list "
		<< "after calling pairWiseSwap()\n";
	printList(start);

	return 0;
}