[Leetcode 141] Linked List Cycle

题目

分析

C代码

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     struct ListNode *next;
* };
*/
bool hasCycle(struct ListNode *head) {
if(head==NULL){
return false;
}
struct ListNode* quick = head;
struct ListNode* slow = head;
do{
if(quick==NULL || quick->next==NULL)
return false;
quick = quick->next->next;
slow = slow->next;
}while(quick!=slow);
return true;
}

C++代码

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
bool hasCycle(ListNode *head) {
if(head==NULL || head->next==NULL){     //空指针和只有一个结点，输出false
return false;
}
ListNode* quick = head;
ListNode* slow = head;
while(quick!=NULL && quick->next!=NULL){  //注意循环结束条件，因为quick每次走两步
quick = quick->next->next;
slow = slow->next;
if(quick == slow){
return true;
}
}
return false;
}
};