二叉树-在二叉树中找到累加和为指定值的最长路径长度

//在二叉树中找到累加和为指定值的最长路径长度
public class Node{
    public int value;
    public Node left;
    public Node right;

    public Node(int data){
        this.value=data;
    }
}

public int getMaxlength(Node head,int sum){
    HashMap<Integer,Integer> sumMap=new HashMap<Integer,Integer>();
    sumMap.put(0,0);
    return preOrder(head,sum,0,1,0,sumMap);
}
public int preOrder(Node head,int sum,int preSum,int level,int maxLen,HashMap<Integer,Integer> sumMap){
    if(head==null){
        return maxLen;
    }
    int curSum=preSum+head.value;
    if(!sumMap.containsKey(curSum)){
        sumMap.put(curSum,level);
    }
    if(sumMap.containsKey(curSum-sum)){
        maxLen=Math.max(level-sumMap.get(curSum-sum),maxLen);
    }
    maxLen=preOrder(head.left,sum,curSum,level+1,maxLen,sumMap);
    maxLen=preOrder(head.right,sum,curSum,level+1,maxLen,sumMap);
    if(level==sumMap.get(curSum)){
        sumMap.remove(curSum);
    }
    return maxLen;
}