题解 | #判断链表中是否有环#

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