title: Linked List Concatenation In O(1) Time
body: <p>I came upon an interesting question and I am puzzled with the answer provided to me. The question is as follows:</p>
  
  <pre><code>The concatenation of 2 lists can be performed O(1) time. 
  Which of the following implementation of list should be used?
  
   - Singly Linked List 
   - Doubly Linked List
   - Circular Linked List
   - Array Implementation Of Linked List
  </code></pre>
  
  <p>I initially thought that a DLL would be the correct choice as concatenation can happen from both side, however the answer seems to CLL. 
  I am confused.
  Any explanation will be most helpful.
  Thanks.</p>