/*

struct TreeNode {

    int val;

    struct TreeNode *left;

    struct TreeNode *right;

    TreeNode(int x) :

            val(x), left(NULL), right(NULL) {

    }

};

*/

class Solution {

public:

    TreeNode* KthNode(TreeNode* pRoot, int k)

    {

   //中序递归

    int count = 0;

    

        if(count > k || pRoot == NULL)

            return NULL;

        TreeNode* p = pRoot;

        stack<TreeNode*> LDRStack;

        TreeNode* kthNode;

        while(p != NULL || !LDRStack.empty()){

            while(p != NULL){

                LDRStack.push(p);

                p = p->left;

            }

            TreeNode* node = LDRStack.top();

            LDRStack.pop();

            count++;

            if(count == k){

                kthNode = node;

            }

            p = node->right;

        }

        return kthNode;

    }

};