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

    TreeLinkNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    public TreeLinkNode GetNext(TreeLinkNode pNode)
    {
        //異常判斷
        if
 
(pNode == null){
            return null;
        }
        //若右子樹不為空，則下一個節點是右子樹的最左子樹節點
        if(pNode.right!=null){
            TreeLinkNode tmp = pNode.right;
            while(tmp.left!=null){
                tmp = tmp.left;
            }
            return tmp;
        }
        
        //若左子樹為空，則依次向上遍歷其父節點，直到某個節點是其父節點的左子樹
 

        TreeLinkNode tmp = pNode;
        while(tmp.next!=null){
            if(tmp.next.left==tmp){
                return tmp.next;
            }
            tmp = tmp.next;
            
        }
        return null;   
    }
}