Flatten the BST into sorted linkedlist

#include<bits/stdc++.h>
using namespace std;



pair<node*,node*>flatten(node*root)
{
    pair<node*,node*>l;
    
    if(root==NULL)
    {
        l.first=NULL;
        l.second=NULL;
        return l;
    }
    
    // leaf node
    
    if(root->left==NULL && root->right==NULL)
       {
           l.first=l.second=root;
           return  l;
       }
    
    if(root->left!=NULL && root->right==NULL)
      {
         pair<node*,node*> p=flatten(root->left);
          p.second->right=root;
          l.first=p.first
          l.second=root;
          return l;
      }
      
      if(root->right!=NULL && root->left==NULL)
      {
          pair<node*,node*>p=flatten(root->right);
          root->right=p.first;
          l.first=root;
          l.second=p.second;
          return l;
          
      }
      
      if(root->left!=NULL && root->right!=NULL)
      {
          pair<node*,node*>ll=flatten(root->left);
          pair<node*,node*>rl=flatten(root->ight);
          ll.second->right=root;
          root->right=rl.first;
          l.first=ll.first;
          l.second=rl.second;
          return l;
      }
    
    
    
    
    
    
}








int main()
{
   
}