力扣141:
给定一个链表,判断链表中是否有环。
如果链表中有某个节点,可以通过连续跟踪 next 指针再次到达该节点,则链表中存在环
如果链表中存在环,则返回 true 。 否则,返回 false 。
package com.lz;
import java.util.HashSet;
import java.util.Set;
public class LinkCycle {
public static class ListNode{
int val;
ListNode next;
public ListNode(int val, ListNode next) {
this.val = val;
this.next = next;
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
ListNode node5,node4,node3,node2,node1;
node5 = new ListNode(5,null);
node4 = new ListNode(4,node5);
node3 = new ListNode(3,node4);
node2 = new ListNode(2,node3);
node1 = new ListNode(1,node2);
node5.next=node3;
System.out.println(hasCycle(node1));
System.out.println(hasCycle2(node1));
}
//迭代
public static boolean hasCycle(ListNode head) {
Set<ListNode> set=new HashSet<>();
while(head!=null) {
if(!set.add(head)) {
return true;
}
head=head.next;
}
return false;
}
//双指针
public static boolean hasCycle2(ListNode head) {
if(head==null||head.next==null) {
return false;
}
ListNode slow=head;
ListNode quick=head.next;
while(slow!=quick) {
if(quick==null||quick.next==null) {
return false;
}
slow=slow.next;
quick=quick.next.next;
}
return true;
}
}