LeetCode - Swap Nodes in Pairs

요즘 재귀에 꽂혀있음.

class Solution {
   public:
   ListNode* swapPairs(ListNode* head) {
      if(!head)  { return head; }
      
      ListNode* first= head;
      ListNode* second = head->next;
      ListNode* dummy = new ListNode(-1);
      
      dummy->next = first;
      ListNode* prev = dummy;
      
      while(second){
         ListNode* temp = second->next;
         
         first->next = second->next;
         second->next = first;
         prev->next = second;
         prev = first;
         
         if(temp){
            first = temp;
            second = temp ->next;
         }
         else break;
      }
      return dummy->next;
   }
};