Python3实现的判断环形链表算法示例

来源：jb51　　时间：2019/3/8 8:39:32　　对本文有异议

本文实例讲述了Python3实现的判断环形链表算法。分享给大家供大家参考，具体如下：

给定一个链表，判断链表中是否有环。

方案一：快慢指针遍历，若出现相等的情况，说明有环

# 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
    """
    slow = fast = head
    while fast and fast.next:
      slow = slow.next
      fast = fast.next.next
      if fast == slow:
        return True
    return False

方案二：遍历链表，寻找.next=head的元素。但超出时间限制

# 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
    """
    if not head:
      return False
    cur = head.next
    while cur:
      if cur.next == head:
        return True
      cur = cur.next
    return False