链表问题——判断一个链表是否为回文结构

import java.util.*;

class test{
class Node{
public Node head;
public int value;
public Node next;

public Node(int data){
this.value = data;
}
}
public static boolean isPalindrom1(Node head){
if(head==null||head.next==null){
return true;
}
Stack<Node> stack = new Stack<Node>();
Node cur = head;
while(cur!=null){
stack.push(cur);
cur = cur.next;
}
while(head!=null){
if(head.value != stack.pop().value){
return false;
}
head = head.next;
}
return true;
}

public static boolean isPalindrom2(Node head){
if(head==null||head.next==null){
return true;
}
Node right = head.next;
Node cur = head;
while(cur.next!=null && cur.next.next!=null){
right = right.next;
cur = cur.next.next;
}
Stack<Node> stack = new Stack<Node>();
while(right!=null){
stack.push(right);
right = right.next;
}
while(!stack.isEmpty()){
if(head.value!=stack.pop().value){
return false;
}
head = head.next;
}
return true;
}

public static boolean isPalindrom3(Node head){
if(head==null || head.next==null){
return true;
}
Node n1 = head;
Node n2 = head;
while(n2.next!=null&&n2.next.next!=null){
n1 = n1.next;
n2 = n2.next.next;
}
Node n3 = n1.next;
n1.next = null;
while(n3!=null){
n2 = n3.next;
n3.next = n1;
n1 = n3;
n3 = n2;
}
n3 = n1;
while(head.next!=null){
if(head.value!=n1.value){
return false;
}
head = head.next;
n1 = n1.next;
}
n1 = n3.next;
while(n3!=null){
n2 = n1.next;
n1.next = n3;
n1 = n2;
n3 = n1.next;
}
return true;
}
}