Pairwise swap elements of a given linked list by changing links | GeeksforGeeks

Given a singly linked list, write a function to swap elements pairwise. For example, if the linked list is 1->2->3->4->5->6->7 then the function should change it to 2->1->4->3->6->5->7

void pairWiseSwap(struct node **head)

{

    // If linked list is empty or there is only one node in list

    if (*head == NULL || (*head)->next == NULL)

        return;

    // Initialize previous and current pointers

    struct node *prev = *head;

    struct node *curr = (*head)->next;

    *head = curr;  // Change head before proceeeding

    // Traverse the list

    while (true)

    {

        struct node *next = curr->next;

        curr->next = prev; // Change next of current as previous node

        // If next NULL or next is the last node

        if (next == NULL || next->next == NULL)

        {

            prev->next = next;

            break;

        }

        // Change next of previous to next next

        prev->next = next->next;

        // Update previous and curr

        prev = next;

        curr = prev->next;

    }

}

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