Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
class Solution(object):
def detectCycle(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
fast = slow = head
while fast and fast.next:
fast = fast.next.next
slow = slow.next
if fast == slow:
break
else:
return None
while head != slow:
slow = slow.next
head = head.next
return head
1 Python 中是None 不是Null也不是null. 代表啥都没有
2 While else
