title: Inserting a vector in a certain position in another vector
body: <p>I want to insert vector <code>b</code> in a certain position in a vector <code>a</code>. For Example</p>
  
  <pre><code>std::vector &lt;int&gt; vecta{ 10, 20, 30 ,40 , 50};
  std::vector &lt;int&gt; vectb{ 1000, 2000, 3000 };
  </code></pre>
  
  <p>How can I have a result vector to be like  {10,20,1000,2000,3000,40,50}  ? 
  I want to remove <code>30</code> and replace its with the vector.</p>