# Can you solve it without using extra space?
from ListNode import ListNode
def linkedListCycleII(head):
if head == None or head.next == None:
return None
dummy = ListNode(0)
dummy.next = head
slow = head
fast = head.next
head = dummy
while slow != fast:
if fast == None or fast.next == None:
return None
slow = slow.next
fast = fast.next.next
while slow != head:
slow = slow.next
head = head.next
return head.val
head = ListNode.cycle()
print linkedListCycleII(head)
