题目
给定1个链表，判断它是不是有环。
样例
给出 ⑵1->10->4->5,tail connects to node index 1，返回 true
分析
判断链表有没有环的问题，很经典，也是面试中常见的问题。
快慢指针解决。
Python代码
"""
Definition of ListNode
class ListNode(object):
def __init__(self,val,next=None):
self.val = val
self.next = next
"""
class Solution:
"""
@param head: The first node of the linked list.
@return: True if it has a cycle,or false
"""
def hasCycle(self,head):
# write your code here
if head == None or head.next == None:
return False
slow = head
fast = head
while fast != None and fast.next != None:
slow = slow.next
fast = fast.next.next
if slow == fast:
return True
return False
GitHub -- Python代码
C++代码
/**
102 带环链表
给定1个链表，判断它是不是有环。
您在真实的面试中是不是遇到过这个题？ Yes
样例
给出 ⑵1->10->4->5,tail connects to node index 1，返回 true
*/
/**
* Definition of ListNode
* class ListNode {
* public:
* int val;
* ListNode *next;
* ListNode(int val) {
* this->val = val;
* this->next = NULL;
* }
* }
*/
class Solution {
public:
/**
* @param head: The first node of linked list.
* @return: True if it has a cycle,or false
*/
bool hasCycle(ListNode *head) {
// write your code here
if(head == NULL || head->next == NULL)
{
return false;
}//if
ListNode *slow = head,*fast = head;
while(fast != NULL && fast->next != NULL)
{
fast = fast->next->next;
slow = slow->next;
if(slow == fast)
{
return true;
}//if
}//while
return false;
}
};
GitHub -- C++代码
