[LeetCode]Linked List Cycle

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

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

利用快慢指针

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