def swapPairs(self, head: ListNode) -> ListNode:
if not head:
return head
next = head.next
if not next:
return head
rest = next.next
next.next = head
head.next = self.swapPairs(rest)
return next
def list_partition(node: ListNode, value: int) -> ListNode:
less = None
bigger = None
while node:
next = node.next
if node.val < value:
node.next = less
less = node
else:
node.next = bigger
bigger = node
node = next
if not less:
return bigger
head = less
while less.next:
less = less.next
less.next = bigger
return head