回文链表

链接： https://www.nowcoder.net/questionTerminal/baefd05def524a92bcfa6e1f113ed4f0
来源：牛客网

请编写一个函数，检查链表是否为回文。

给定一个链表ListNode* pHead，请返回一个bool，代表链表是否为回文。

测试样例：

{1,2,3,2,1}

返回：true

{1,2,3,2,3}

返回：false

import java.util.*;

public class Main {

	/**
	 * @param args
	 */
	
	public static class ListNode {
	    int val;
	    ListNode next = null;

	    ListNode(int val) {
	        this.val = val;
	    }
	}
	
	public static void main(String[] args){
		ListNode p1 = new ListNode(1);
		p1.next = new ListNode(2);
		p1.next.next = new ListNode(3);
		p1.next.next.next = new ListNode(2);
		p1.next.next.next.next = new ListNode(1);
		System.out.println(isPalindrome(p1));
		
	}
	
	
	
	 public static boolean isPalindrome(ListNode pHead) {
	        // write code here
		 ListNode slow = pHead;
		 ListNode fast = pHead;
		 StringBuffer on1 = new StringBuffer();
		 StringBuffer on2 = new StringBuffer();
		 while(true){
			 if(fast.next==null){
				 break;
			 }
			 if(fast.next.next==null){
				 slow = slow.next;
				 break;
			 }
			 on1.append(slow.val);
			 slow = slow.next;
			 fast = fast.next.next;
		 }
		 slow = slow.next;
		 while(slow!=null){
			 on2.append(slow.val);
			 slow = slow.next;
		 }
		 
		 on1.reverse();
		 return on1.toString().equals(on2.toString()); 
	   }
	
	
		
		
		
	
	

}