题解 | #判断链表中是否有环#
判断链表中是否有环
http://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9
头部指针的表达
在这道题中,Head指针用的也是ListNode的结构。
这里用到快慢指针。
# class ListNode: # def __init__(self, x): # self.val = x # self.next = None # # # @param head ListNode类 # @return bool布尔型 # class Solution: def hasCycle(self , head ): # write code here if head is None or head.next is None: return False walker = head runner = head.next while runner is not None and walker != runner: walker = walker.next runner = runner.next if runner!=None: runner = runner.next if runner==walker: return True return False