题解 | #牛牛的冒险旅程#

import numbers
import re
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @return int整型
#
from functools import reduce
class Solution:
    def gcdInCycle(self , head: ListNode) -> int:
        # write code here
        nums=[]
        cur=head
        dic={}
        while cur:
            if not dic.get(cur.val):
                dic[cur.val]=1
            else:
                nums.append(cur.val)
                dic[cur.val]+=1
                if dic[cur.val]==3:
                    return reduce(self.gcd,nums)
            cur=cur.next
        return -1
    
    def gcd(self,x,y):
        while y:
            x,y=y,x%y
        return x