reverseLLPairs.cpp

/*
Program     : Reverse the Linked List in Pairs. (Q3: Assignment 1)
Author      : © Vipin Kumar
Created on  : March 20, 2018 11:38 IST
*/

#include <iostream>
#include <conio.h>
#include <cstdlib>

using namespace std;

struct node {
	int data;
	node* next;
};


class SinglyLinkedList {
public:
	node * head;
	int data;
	int size;

	SinglyLinkedList ();
	~SinglyLinkedList ();
	void insertion (int);
	void swapPairs (node*);
	void display ();

};


SinglyLinkedList::SinglyLinkedList () {
	head = NULL;
	size = 0;
}


SinglyLinkedList::~SinglyLinkedList () {
	node* temp;
	while (head->next != NULL) {
		temp = head;
		head = head->next;
		delete temp;
	}
}


void SinglyLinkedList::insertion (int value) {
	node* newNode = new node;
	newNode->data = value;
	newNode->next = NULL;

	node* temp;

	if (head == NULL) {
		head = newNode;
	}

	else {
		temp = head;
		while (temp->next != NULL) {
			temp = temp->next;
		}
		temp->next = newNode;
	}
	size++;
}


void swapData (int *a, int *b) {
	int temp;
	temp = *a;
	*a = *b;
	*b = temp;
}


void SinglyLinkedList:: swapPairs (node* head) {
	if (head != NULL && head->next != NULL) {
		swapData (&head->data, &head->next->data);
		swapPairs (head->next->next);
	}
}


void SinglyLinkedList::display () {
	node* temp = head;

	if (head == NULL) {
		cout << "Linked List is EMPTY.\n";
	}

	else if (head->next == NULL) {
		cout << head->data;
	}

	else {
		while (temp->next != NULL) {
			cout << temp->data << "->";
			temp = temp->next;
		}
		cout << temp->data;
	}
}


int main () {
	SinglyLinkedList sll;
	sll.insertion (1);
	sll.insertion (2);
	sll.insertion (3);
	sll.insertion (4);
	sll.insertion (5);
	sll.insertion (6);

	sll.display ();
	cout << '\n';
	sll.swapPairs (sll.head);
	sll.display ();
	getch ();
	return 0;
}