Linked List Cycle详解程序员

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; 
         
    } 
}