C++ Program For Swapping Nodes In A Linked List Without Swapping Data

// C++ program to swap the nodes of linked list rather
// than swapping the field from the nodes.
#include <bits/stdc++.h>
using namespace std;

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

// Function to swap nodes x and y in 
// linked list by changing links 
void swapNodes(Node** head_ref, 
               int x, int y)
{
    // Nothing to do if x and y 
    // are same
    if (x == y)
        return;

    // Search for x (keep track of 
    // prevX and CurrX
    Node *prevX = NULL, 
         *currX = *head_ref;
    while (currX && currX->data != x) 
    {
        prevX = currX;
        currX = currX->next;
    }

    // Search for y (keep track of 
    // prevY and CurrY
    Node *prevY = NULL,
         *currY = *head_ref;
    while (currY && currY->data != y) 
    {
        prevY = currY;
        currY = currY->next;
    }

    // If either x or y is not present, 
    // nothing to do
    if (currX == NULL || 
        currY == NULL)
        return;

    // If x is not head of linked list
    if (prevX != NULL)
        prevX->next = currY;
    else 

        // Else make y as new head
        *head_ref = currY;

    // If y is not head of linked list
    if (prevY != NULL)
        prevY->next = currX;
    else // Else make x as new head
        *head_ref = currX;

    // Swap next pointers
    Node* temp = currY->next;
    currY->next = currX->next;
    currX->next = temp;
}

// Function to add a node at the
// beginning of 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->6->7 */
    push(&start, 7);
    push(&start, 6);
    push(&start, 5);
    push(&start, 4);
    push(&start, 3);
    push(&start, 2);
    push(&start, 1);

    cout << "Linked list before calling swapNodes() ";
    printList(start);
    swapNodes(&start, 4, 3);
    cout << "Linked list after calling swapNodes() ";
    printList(start);
    return 0;
}
// This is code is contributed by rathbhupendra

// C++ program to swap two given nodes 
// of a linked list
#include <iostream>

using namespace std;

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

    // constructor
    Node(int val, Node* next)
        : data(val)
        , next(next)
    {
    }

    // print list from this
    // to last till null
    void printList()
    {
        Node* node = this;

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

        cout << endl;
    }
};

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

void swap(Node*& a, Node*& b)
{
    Node* temp = a;
    a = b;
    b = temp;
}

void swapNodes(Node** head_ref, 
               int x, int y)
{
    // Nothing to do if x and 
    // y are same
    if (x == y)
        return;

    Node **a = NULL, **b = NULL;

    // Search for x and y in the linked list
    // and store their pointer in a and b
    while (*head_ref) 
    {
        if ((*head_ref)->data == x) 
        {
            a = head_ref;
        }

        else if ((*head_ref)->data == y) 
        {
            b = head_ref;
        }

        head_ref = &((*head_ref)->next);
    }

    // If we have found both a and b
    // in the linked list swap current
    // pointer and next pointer of these
    if (a && b) 
    {
        swap(*a, *b);
        swap(((*a)->next), ((*b)->next));
    }
}

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

    // The constructed linked list is:
    // 1->2->3->4->5->6->7
    push(&start, 7);
    push(&start, 6);
    push(&start, 5);
    push(&start, 4);
    push(&start, 3);
    push(&start, 2);
    push(&start, 1);

    cout << "Linked list before calling swapNodes() ";
    start->printList();
    swapNodes(&start, 6, 1);
    cout << "Linked list after calling swapNodes() ";
    start->printList();
}