def swapPairsRec(self, head: ListNode) -> ListNode:
if not head or not head.next:
return head
n = head.next
head.next = self.swapPairsRec(n.next)
n.next = head
return n
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
s1, s2 = [], []
while l1:
s1.append(l1.val)
l1 = l1.next
while l2:
s2.append(l2.val)
l2 = l2.next
dummy, carry = ListNode(), 0
for e1, e2 in zip_longest(s1[::-1], s2[::-1]):
s = carry
if e1:
s += e1
if e2:
s += e2
carry = s // 10
dummy.next = ListNode(s % 10, dummy.next)
if carry == 1:
dummy.next = ListNode(1, dummy.next)
return dummy.next
def insertionSortList(self, head: ListNode) -> ListNode:
prev = sentinal = ListNode()
while head:
nxt = head.next
# Optimization: search from begining
# only when head is supposed in front of last insert point
if head.val <= prev.val:
prev = sentinal
while prev.next and prev.next.val < head.val:
prev = prev.next
head.next = prev.next
prev.next = head
head = nxt
return sentinal.next