// Java program to swap two given nodes of a linked list

public class Solution {

    // Represent a node of the singly linked list

    class Node {

        int data;

        Node next;

        public Node(int data)

        {

            this.data = data;

            this.next = null;

        }

    }

    // Represent the head and tail of the singly linked list

    public Node head = null;

    public Node tail = null;

    // addNode() will add a new node to the list

    public void addNode(int data)

    {

        // Create a new node

        Node newNode = new Node(data);

        // Checks if the list is empty

        if (head == null) {

            // If list is empty, both head and

            // tail will point to new node

            head = newNode;

            tail = newNode;

        }

        else {

            // newNode will be added after tail such that

            // tail's next will point to newNode

            tail.next = newNode;

            // newNode will become new tail of the list

            tail = newNode;

        }

    }

    // swap() will swap the given two nodes

    public void swap(int n1, int n2)

    {

        Node prevNode1 = null, prevNode2 = null,

             node1 = head, node2 = head;

        // Checks if list is empty

        if (head == null) {

            return;

        }

        // If n1 and n2 are equal, then

        // list will remain the same

        if (n1 == n2)

            return;

        // Search for node1

        while (node1 != null && node1.data != n1) {

            prevNode1 = node1;

            node1 = node1.next;

        }

        // Search for node2

        while (node2 != null && node2.data != n2) {

            prevNode2 = node2;

            node2 = node2.next;

        }

        if (node1 != null && node2 != null) {

            // If previous node to node1 is not null then,

            // it will point to node2

            if (prevNode1 != null)

                prevNode1.next = node2;

            else

                head = node2;

            // If previous node to node2 is not null then,

            // it will point to node1

            if (prevNode2 != null)

                prevNode2.next = node1;

            else

                head = node1;

            // Swaps the next nodes of node1 and node2

            Node temp = node1.next;

            node1.next = node2.next;

            node2.next = temp;

        }

        else {

            System.out.println("Swapping is not possible");

        }

    }

    // display() will display all the

    // nodes present in the list

    public void display()

    {

        // Node current will point to head

        Node current = head;

        if (head == null) {

            System.out.println("List is empty");

            return;

        }

        while (current != null) {

            // Prints each node by incrementing pointer

            System.out.print(current.data + " ");

            current = current.next;

        }

        System.out.println();

    }

    public static void main(String[] args)

    {

        Solution sList = new Solution();

        // Add nodes to the list

        sList.addNode(1);

        sList.addNode(2);

        sList.addNode(3);

        sList.addNode(4);

        sList.addNode(5);

        sList.addNode(6);

        sList.addNode(7);

        System.out.println("Original list: ");

        sList.display();

        // Swaps the node 2 with node 5

        sList.swap(6, 1);

        System.out.println("List after swapping nodes: ");

        sList.display();

    }

}