old_contents: sd dsds 
new_contents: # Definition for singly-linked list.
  # class ListNode:
  #     def __init__(self, val=0, next=None):
  #         self.val = val
  #         self.next = next
  class Solution:
      def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
          if not head or not head.next:
              return head
          
          tempNextNext = head.next.next
          next = head.next
          tmpHead = head
          
          head.next.next = head
          head = head.next
          head.next.next = self.swapPairs(tempNextNext)
          
          return head
subject: swap node pairs