# 141. Linked List Cycle """ given the 'head' of a linked list, determine if the linked list has a cycle in it. there is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the 'next' pointer. internally, 'pos' is used to denote the index of the node that tail's 'next' pointer is connected to. note that 'pos' is not passed as a parameter. return true if there is a cycle in the linked list. otherwise return false. """ # Definition for singly-linked list. class ListNode(object): def __init__(self, x): self.val = x self.next = None class Solution(object): def hasCycle(self, head): """ :type head: ListNode :rtype: bool """ fast = slow = head while fast and fast.next: slow, fast = slow.next, fast.next.next if fast == slow: return True return False if __name__ == "__main__": obj = Solution()