Linked List Cycle

问题描述:

Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

代码实现：

/** * 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) {        if(head==null) return false;        ListNode fast=head;        ListNode slow=head;                do{            if(fast!=null) fast=fast.next;            if(slow!=null) slow=slow.next;            if(fast != null){                fast=fast.next;            }else{                return false;            }        }while(fast != slow);        return true;            }}