二叉搜索树的第k个结点

    TreeNode* KthNode(TreeNode* pRoot, int k)
    {
        if(pRoot == NULL || k == 0)
            return NULL;
        return KthNodeCore(pRoot,k);
    }
    TreeNode* KthNodeCore(TreeNode* pRoot , int& k)
    {
        TreeNode* target = NULL;
        if(pRoot->left)
        {
            target = KthNodeCore(pRoot->left , k);
        }
        if(target == NULL)
        {
            if(k == 1)
                target = pRoot;
            k--;
        }
        if(target == NULL && pRoot->right)
             target = KthNodeCore(pRoot->right , k);
        return target;
    }