def hasCycle2(self, head: ListNode) -> bool:
"""
不需要额外空间
"""
while head:
if head.val is None:
return True
head.val = None
# listNode 的值不会为 None，所以这里赋值以后如果下一个循环
# head.val 为 None，则认为进入了循环
head = head.next
return False
def add_two_numbers(l1, l2):
s1, s2 = [], []
tmp1 = l1
while tmp1:
s1.append(tmp1.val)
tmp1 = tmp1.next
tmp1 = l2
while tmp1:
s2.append(tmp1.val)
tmp1 = tmp1.next
head = ListNode(0)
sum = 0
while s1 or s2:
if s1: sum += s1.pop()
if s2: sum += s2.pop()
head.val = sum % 10 # assign the current value to the exist node and create a new node for the carry value
cur = ListNode(sum // 10)
cur.next = head
head = cur
sum //= 10
return head if head.val != 0 else head.next
def deleteNode(self, node: ListNode):
node.val = node.next.val
node.next = node.next.next
def delete_node(node: ListNode):
node.val, node.next = node.next.val, node.next.next
