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)
    {
        TreeLinkNode * rev;
        if(pNode==NULL)
            return NULL;
        if(pNode->right!=NULL)
        {
            rev=pNode->right;
            while(rev->left!=NULL)
                rev=rev->left;
            return rev;
        }
        else
        {
            if(pNode->next==NULL)
            {
                return NULL;
            }
            if(pNode->next->left==pNode)
            {
                return pNode->next;
            }
            rev=pNode;
            while(rev->next!=NULL&&rev==rev->next->right)
            {
                rev=rev->next;
            }
            return rev->next;
        }
    }
};