class Solution:
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
cur = dummy = ListNode(0)
while l1 and l2:
if l1.val < l2.val:
cur.next = l1
l1 = l1.next
else:
cur.next = l2
l2 = l2.next
cur = cur.next
cur.next = l1 if l1 else l2
return dummy.next