LeetCode 11 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?

分析：快慢指针法

/**
* 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) {
ListNode fast = head;
ListNode slow = head;
boolean hasCircle = false;
while(fast != null && fast.next != null){
fast = fast.next.next;
slow = slow.next;
//find the meet point
if(fast == slow){
hasCircle = true;
break;
}
}
return hasCircle;
}
}