title: difference between two linked lists, O(N)
body: <p>I have two linked lists with unique but with the same elements in shuffled order.</p>
  
  <p>Then random element gets deleted from list1. How can I determine deleted element?</p>
  
  <p>Example:</p>
  
  <blockquote>
    <p>list1 <strong>0 3 7 8 1</strong></p>
    
    <p>list2 <strong>3 7 8 1 0</strong></p>
  </blockquote>
  
  <p>..deleting..</p>
  
  <blockquote>
    <p>list1 <strong>- 3 7 8 1</strong></p>
    
    <p>list2 <strong>3 7 8 1 0</strong></p>
  </blockquote>
  
  <p>Answer: <strong>0</strong></p>
  
  <p>The most important part is that I need to do it by <strong>O(N).</strong></p>