二叉树的下一个结点

/*
struct TreeLinkNode {
int val;
struct TreeLinkNode *left;
struct TreeLinkNode *right;
struct TreeLinkNode *next;
TreeLinkNode(int x) :val(x), left(NULL), right(NULL), next(NULL) {

}
};
*/
class Solution {
public:
TreeLinkNode* GetNext(TreeLinkNode* pNode) {
if (pNode == NULL) return NULL;
if (pNode->right != NULL) {
pNode = pNode->right;
while(pNode->left != NULL) {
pNode = pNode->left;
}
return pNode;
}
//如果没有右孩子，
//则找当前结点的父结点，的父节点；
//next 表示父节点
while (pNode->next != NULL) {
TreeLinkNode* pRoot = pNode->next;
if (pRoot->left == pNode)
return pRoot;
pNode = pNode->next;
}
return NULL;
}
};