# 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]:
        prev = root = ListNode(None)
        prev.next = head
        
        while head and head.next:
            point = head.next
            head.next = point.next
            point.next = head
            prev.next = point
            
            head= head.next
            prev= prev.next.next
        
        return root.next