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;

}
}