1 题目
给定一个链表,判断链表中是否有环
https://leetcode-cn.com/problems/linked-list-cycle/
2 Java
2.1 方法一(HashSet查重)
/**
* 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) {
HashSet<ListNode> set = new HashSet<>();
// 遍历链表
while(head != null){
// 操作
if(set.contains(head)) return true;
set.add(head);
// 下一节点
head = head.next;
}
return false;
}
}
2.2 方法二(相遇指针)
/**
* 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 || head.next == null) return false;
ListNode slow = head;
ListNode fast = head.next;
// 两指针未相遇,循环
while(slow != fast){
if(fast.next == null || fast.next.next == null) return false;
// 指针1移动
slow = slow.next;
// 指针2移动
fast = fast.next.next;
}
return true;
}
}