linked-list-cycle

题目描述

Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?

思路

使用快慢指针,如果有环必定会相遇

代码

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    //快慢指针判断是否有环
    public boolean hasCycle(ListNode head) {
        if(head==null||head.next==null){
            return false;
        }
        ListNode fast = head;
        ListNode slow = head;
        while (fast.next!=null&&fast.next.next!=null){
            fast=fast.next.next;
            slow=slow.next;
            if(fast==slow){
                return true;
            }
        }
        return false;
    }
}