SwapNodes.cpp

class Solution {

public:

    ListNode* swapPairs(ListNode* head) {

        // if head is NULL OR just having a single node, then no need to change anything 

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

        {

            return head;

        }

            

        ListNode* temp; // temporary pointer to store head -> next

        temp = head->next; // give temp what he want

        

        head->next = swapPairs(head->next->next); // changing links

        temp->next = head; // put temp -> next to head

        

        return temp; // now after changing links, temp act as our head

    }

};