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C++ Program For Pairwise Swapping Elements Of A Given Linked List

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  • Last Updated : 15 Dec, 2021
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Given a singly linked list, write a function to swap elements pairwise.

Input: 1->2->3->4->5->6->NULL 
Output: 2->1->4->3->6->5->NULL Input: 1->2->3->4->5->NULL 
Output: 2->1->4->3->5->NULL Input: 1->NULL 
Output: 1->NULL 

For example, if the linked list is 1->2->3->4->5 then the function should change it to 2->1->4->3->5, and if the linked list is then the function should change it to. 

METHOD (Iterative): 
Start from the head node and traverse the list. While traversing swap data of each node with its next node’s data. 
Below is the implementation of the above approach:

C++




// 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()";
    printList(start);
  
    pairWiseSwap(start);
  
    cout << "Linked list " << 
            "after calling pairWiseSwap()";
    printList(start);
  
    return 0;
}
// This code is contributed by rathbhupendra


Output:

Linked list before calling pairWiseSwap()
1 2 3 4 5 
Linked list after calling pairWiseSwap()
2 1 4 3 5 

Time complexity: O(n)
Please refer complete article on Pairwise swap elements of a given linked list for more details!


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