Tree traversal and return vector list.

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//In case your pre, in, post-order traversal function wants you to return the list, not to print them.
create another function lst1, and pass vector with refernce.

void lst1(struct Node*root, vector<int> &v)
{
    if (root==0)
    return;
    else
    v.push_back(root->data);
    lst1(root->left,v);
    lst1(root->right,v);
}
vector <int> preorder(Node* root)
{
  vector<int>v;
  lst1(root,v);
  return v;
}

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