思想创建两个游标,一快一慢,相遇后慢游标回到链表头节点,快游标放慢,然后快慢游标会在链表环的头部相遇
class Node(object):
'''创建一个节点'''
def __init__(self,item):
self.item = item
self.next = None
def findloop(head):
slow = head
fast = head
loopExist = False
# 创建一个标记
if head == None:
return False
# 如果头节点为空,直接返回
while fast.next!=None and fast.next.next != None:
# 只要两个游标不为空就一直循环
# 两个游标一快一慢,终会相遇
fast = fast.next.next
# 快游标
slow = slow.next
# 慢游标
if slow == fast:
# 游标相遇,返回True,并跳出循环
loopExist=True
break
if loopExist == True:
# 如果相遇,说明有环
slow = head
# 将慢游标从头节点重新开始
while slow != fast:
# 两个游标不相等就一直循环
slow = slow.next
fast = fast.next
return slow.item
# 相等以后,返回环的头节点
return False
node1 = Node(1)
node2 = Node(2)
node3 = Node(3)
node4 = Node(4)
node1.next = node2
node2.next = node3
node3.next = node4
if findloop(node1):
print('存在环')
print(findloop(node1))
else:
print("不存在环结构")