暴力解法:直接中序遍历然后找i+1即可

public class TreeLinkNode {
    int val;
    TreeLinkNode left = null;
    TreeLinkNode right = null;
    TreeLinkNode next = null;

    TreeLinkNode(int val) {
        this.val = val;
    }
}
*/
import java.util.*;
public class Solution {
    Vector<TreeLinkNode> v =new Vector();
    public TreeLinkNode GetNext(TreeLinkNode pNode) {
        TreeLinkNode tmp = pNode;
        while(tmp.next != null){
            tmp = tmp.next;
        }
        inorder(tmp);
        for (int i = 0; i < v.size()-1 ; i++) {
            if(v.get(i) == pNode){
                return v.get(i+1);
            }
        }
        return null;
    }
    
    public void inorder(TreeLinkNode node){
        if(node != null){
            inorder(node.left);
            v.add(node);
            inorder(node.right);
        }
    }
}