/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* pre;
    TreeNode* dumpy;
    TreeNode* convertBiNode(TreeNode* root) {
        pre = new TreeNode(-1);
        dumpy = pre;
        inorder(root);
        return dumpy->right;
    }
    void inorder(TreeNode* root){
        if(root == NULL) return ;
        inorder(root->left);
        pre->right = root;
        root->left = nullptr;
        pre = root;
        inorder(root->right);
    }
};