increasing-order-search-tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> vec;
    void helper(TreeNode* root){
        if(root==nullptr) return;
        helper(root->left);
        vec.push_back(root->val);
        helper(root->right);
    }
    TreeNode* increasingBST(TreeNode* root) {
        helper(root);
        TreeNode* r = new TreeNode(0);
        TreeNode* curr=r;
        for(auto v : vec){
            curr->right=new TreeNode(v);
            curr=curr->right;
        }
        return r->right;
    }
};