Open In App
Related Articles

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

Improve Article
Save Article
Like Article

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++ program to pairwise swap elements
// in a given linked list
#include <bits/stdc++.h>
using namespace std;
// A linked list node
class Node 
    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 */
        // 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()";
    cout << "Linked list " << 
            "after calling pairWiseSwap()";
    return 0;
// This code is contributed by rathbhupendra


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

Time complexity: O(n) 

Auxiliary Space: O(1)

Please refer complete article on Pairwise swap elements of a given linked list for more details!

Last Updated : 17 Aug, 2023
Like Article
Save Article
Similar Reads
Related Tutorials