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Pairwise swap of nodes in LinkedList

Tags : linkedlist, geeksforgeeks, cpp, easy

Problem Statement - link #

Given a linked list of N positive integers. You need to swap elements pairwise. Your task is to complete the function pairwise_swap().

Your Task: You don’t have to worry about input and output, you just have to complete the function pairwise_swap(). The printing is done automatically by the driver code.

Expected Time Complexity: O(N) Expected Auxiliary Space: O(1)

Examples #

Example 1:

Input:
N = 7
value[] = {1,2,3,4,5,6,7}
Output: 2 1 4 3 6 5 7
Explanation:The linked list after swapping
becomes: 1 2 3 4 5 6 7 -> 2 1 4 3 6 5 7.

Example 2:

Input:
N = 6
value[] = {1,2,3,4,5,6}
Output: 2 1 4 3 6 5
Explanation:The linked list after swapping
becomes: 1 2 3 4 5 6 -> 2 1 4 3 6 5.

Constraints #

Solutions #

class Solution{
    public:
    //Function to swap elements pairwise.
    struct Node* pairwise_swap(struct Node* head)
    {
        // your code here
        if(head==NULL || head->next==NULL) return head;
        Node* curr = head->next->next;
        Node* prev = head->next;
        prev->next = head;
        head->next = curr;
        head = prev;
        prev = head->next;
        while(curr != NULL && curr->next != NULL) {
            Node* temp = curr->next;
            curr->next = curr->next->next;
            temp->next = curr;
            curr = curr->next;
            prev->next = temp;
            prev = temp->next;
        }
        return head;
    }
};