Linked List Cycle
Linked List Cycle
Given a linked list, determine if it has a cycle in it.
c++
/** * 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) { /* 1. 空链表不成环 2. 一个节点自环 3. 一条链表完整成环 */ if(head==NULL)return false; if(head->next==NULL)return false; if(head->next==head)return true; ListNode* y=head->next; ListNode* x=head->next->next; while(x!=NULL && y!=NULL) { x=x->next; if(x==NULL)break; x=x->next; y=y->next; if(x==y)break; } return x==y; } };
java版:
/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * * **/ public class Solution { public boolean hasCycle(ListNode head) { ListNode slow=head; ListNode fast=head; while(fast!=null&&fast.next!=null){ slow=slow.next; fast=fast.next.next; if(slow==fast) return true; } return false; } }