title: find crossing line through 3 points on horizontal lines
body: <p>Given a group of n points which are spread on 3 horizontal lines (y=0 , y=1, y=2)
  think of algorithm to find if there is crossing line with O(n^2)</p>
  
  <p><a href="http://i.stack.imgur.com/kRsvQ.jpg" rel="nofollow">enter image description here</a></p>