def addTwoNumbers2(self, l1: ListNode, l2: ListNode) -> ListNode:
"""
Regular solution using a stack.
"""
def get_stack(l: ListNode) -> List[int]:
stack, curr = [], l
while curr:
stack.append(curr.val)
curr = curr.next
return stack
s1, s2 = get_stack(l1), get_stack(l2)
carry, nextNode = 0, None
while s1 or s2 or carry:
curr = 0
if s1:
curr += s1.pop()
if s2:
curr += s2.pop()
carry, curr = divmod(curr + carry, 10)
currNode = ListNode(curr)
currNode.next = nextNode
nextNode = currNode
return nextNode
def removeNthFromEnd(self, head: 'ListNode', n: 'int') -> 'ListNode':
refDict = {}
cnt = 0
fakeHead = ListNode(None)
fakeHead.next = head
while fakeHead is not None:
cnt += 1
refDict[cnt] = fakeHead
fakeHead = fakeHead.next
# When list is too short, return the original list head directly.
if cnt > n:
# The node to be deleted is stored at refDict[cnt - n + 1].
refDict[cnt - n].next = refDict.get(cnt - n + 2)
return refDict[1].next
def deleteNode(self, node: ListNode):
node.val = node.next.val
node.next = node.next.next