在二叉树中找到累加和为指定值的最长路径长度

import java.util.*;
//在二叉树中找到累加和为指定值的最长路径长度
public class SumMaxLen{
	//二叉树节点的定义
	public static class Node{

		public int value;
		public Node left;
		public Node right;

		public Node(int data)
		{

			this.value=data;
		}

	}
   //获取指定值的最长路径长度
   public static int sumMaxLen(Node head,int sum)
   {     //存储当前节点最长路径值和所在的层数
         HashMap<Integer,Integer>sumMap=new HashMap<Integer,Integer>();
         sumMap.put(0,0);//没有遍历节点
         return preOrder(head,sum,0,1,0,sumMap);

   }
   //利用二叉树前序遍历
   public static int preOrder(Node head,int sum,int preSum,int level
   	,int maxLen,HashMap<Integer,Integer>sumMap)
   {
     
     if(head==null)
     {
       return maxLen; //记录其中的最大值
     }
     //当前节点的最大值计算
     int curSum=preSum+head.value;
     //集合中不存在当前值
     if(!sumMap.containsKey(curSum))
     {
     	sumMap.put(curSum,level);
     }
     //更新最大长度
     if(sumMap.containsKey(curSum-sum))
     {
     	//取两者的最大值
     	maxLen=Math.max(level-sumMap.get(curSum-sum),maxLen);
     }
     //递归调用
     maxLen=preOrder(head.left,sum,curSum,level+1,maxLen,sumMap); //左子树
     maxLen=preOrder(head.right,sum,curSum,level+1,maxLen,sumMap); //右子树
     if(level==sumMap.get(curSum))
     {
     	sumMap.remove(curSum);
     }
     return maxLen;
   }
   public static void main(String[]args)
   {
   	/**
   	    -3
   	 3      -9
   1   0   2   1
     1  6
   	*/
     Node node =new Node(-3);
     node.left=new Node(3);
     node.right=new Node(-9);
     node.left.left=new Node(1);
     node.left.right=new Node(0);
     node.right.left=new Node(2);
     node.right.right=new Node(1);
     node.left.right.left=new Node(1);
     node.left.right.right=new Node(6);
     
     System.out.println("最长路径为:"+sumMaxLen(node,6));
     System.out.println("最长路径为:"+sumMaxLen(node,-9));
   }

}