# 判断单向列表是否包括环，若包含，环入口的节点和环长计算

``````''' 判断单向列表是否包括环，若包含，环入口的节点和环长计算 '''

#定义链表
class ListNode():
def __init__(self, val=None):
self.val = val
self.next = next

#判断链表是否有环(如果没有环则输出False，如果有环则输出(环的入口点地址,环入口点值,环长))
loopExist = False
print('no exist loop!')
return loopExist
slowstepnum = 0 #记录slow从开始到相遇走的步长
faststepnum = 0 #记录fast从开始到相遇走的步长
while fast.next != None and fast.next.next!=None:
slow = slow.next
fast = fast.next.next
slowstepnum += 1
faststepnum += 2
if slow == fast:
loopExist = True
print('exist loop!')
break
looplength = faststepnum - slowstepnum #环长 = fast走的步长 - slow走的步长
#判断环入口点(相遇点到环入口点和开始点到环入口点长度相同)
if loopExist:
while slow != fast:
slow = slow.next
fast = fast.next
return (slow, slow.val, looplength)

print('no exist loop!')
return loopExist

if __name__ == "__main__":
L1 = ListNode(1)
L2 = ListNode(2)
L3 = ListNode(3)
L4 = ListNode(4)
L5 = ListNode(5)
L6 = ListNode(6)
L7 = ListNode(7)
L8 = ListNode(8)
L1.next = L2
L2.next = L3
L3.next = L4
L4.next = L5
L5.next = L6
L6.next = L7
L7.next = L8
L8.next = L3
print(findloop(L1))

``````
原文作者：微微心情smile
原文地址: https://blog.csdn.net/u012564409/article/details/79565346
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