title: Is there a way to find if path exists in a Directed acyclic graph in constant time (O(1))?
body: <p>I have some directed acyclic graph. I want to find if path exists between two vertices in <code>O(1)</code>. </p>
  
  <p>Also, I want to add and remove edges between two vertices in <code>O(n^2)</code>. </p>
  
  <p>I think, I need to store information, how many path exists between two nodes. But I don't come up full algorithm.</p>