LeetCode Linked List Cycle (Floyd判圈算法)

题目描述：https://oj.leetcode.com/problems/linked-list-cycle/

给一个链表，Floyd判圈可在O（n）的时间复杂度，O（1）的空间复杂度内判定其中有没有环。

package LinkedListCycle;

public class Solution {
class ListNode{
int val;
ListNode next;
ListNode(int x){
val = x;
next = null;
}
}
public boolean hasCycle(ListNode head) {
if(head==null) return false;
ListNode slowPtr = head;
ListNode fastPtr = head;
boolean flag = true;
do{
if(fastPtr.next == null ||fastPtr.next.next == null){
flag = false;
break;
}
slowPtr = slowPtr.next;
fastPtr = fastPtr.next.next;
}while(slowPtr != fastPtr);
return flag;
}
}