二叉搜索树的第K个节点

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    stack<TreeNode*>node;
    TreeNode* KthNode(TreeNode* pRoot, unsigned int k)
    {
        if(pRoot == NULL||k<=0)
            return NULL;
        node.push(pRoot);
        TreeNode *p = NULL;
        while(!node.empty())
        {
            while(pRoot->left != NULL)
            {
                  pRoot=pRoot->left;
                  node.push(pRoot);
            }
            while(!node.empty())
            {
                 p = node.top();
                 node.pop();
                  --k;
                 if(k == 0)
                     return p;
                 if(p->right !=NULL)
                 {
                      node.push(p->right);
                      pRoot = p->right;
                      break;
                  }
            }
            
        }
        
        return NULL;
    }

    
};