Detect Linked List Cycle

Hi, here's your problem today. This problem was recently asked by Uber:

Given a linked list, determine if the linked list has a cycle in it. For notation purposes, we use an integer pos which represents the zero-indexed position where the tail connects to.

Example:
Input: head = [4,3,2,1,0], pos = 1.
Output: true
The example indicates a list where the tail connects to the second node.

class ListNode(object):

  def __init__(self, x):

    self.val = x

    self.next = None



class Solution(object):

  def hasCycle(self, head):

    # Fill this in.



testHead = ListNode(4)

node1 = ListNode(3)

testHead.next = node1

node2 = ListNode(2)

node1.next = node2

node3 = ListNode(1)

node2.next = node3

testTail = ListNode(0)

node3.next = testTail

testTail.next = node1



print(Solution().hasCycle(testHead))

# True