LeetCode--141--环形链表

问题描述：

给定一个链表，判断链表中是否有环。

思路：用快的指针追慢的指针，只要有圈，一定能追上。

错误:

 1 class Solution(object):
 2     def hasCycle(self, head):
 3         """
 4         :type head: ListNode
 5         :rtype: bool
 6         """
 7         if head == None or head.next == None:
 8             return False
 9         p = head.next
10         q = head.next.next
11         while p and q:
12             if p == q:
13                 return True
14             p = p.next
15             if q.next != None:
16                 q = q.next.next
17         return False

改正：

 1 class Solution(object):
 2     def hasCycle(self, head):
 3         """
 4         :type head: ListNode
 5         :rtype: bool
 6         """
 7         if head == None or head.next == None:
 8             return False
 9         p = head.next
10         q = head.next.next
11         while q and q.next:
12             if p == q:
13                 return True
14             p = p.next
15             q = q.next.next
16         return False

2018-09-12 21:03:17