Swap Nodes in Pairs

https://leetcode.com/problems/swap-nodes-in-pairs/

 

 class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
       if(!head || !head->next) return head;
        ListNode* temp;
        temp = head->next;
        head->next = swapPairs(head->next->next);
        temp->next = head;
        
        return temp;
    }
};

 

  // We use a dummy head node to make handling head operations simpler
        ListNode *dummy = new ListNode(-1), *tail = dummy;
        // add the dummy node to list
        tail->next = head;
        
        while(head && head->next) {
            ListNode *nextptr = head->next->next;
            // swap the adjacent nodes
            // 2nd node comes to 1st pos
            tail->next = head->next;
            // connecting 2nd node to 1st node
            (head->next)->next = head;
            // make the 1st node connected to next node on list
            tail = head;
            tail->next = nextptr;
            head = nextptr;
        }
        
        head = dummy->next;
        delete dummy;
        return head;