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));   }}