title: Find if list of coordinates form a loop
body: <p>So I have a list of points that generally form a sort of circular shape except there are often little offshoots from the circle that are essentially just lines from say the border of the circle going in a certain direction. I want to create a function that when given this list of coordinates/points finds whether there exists a complete path in this set of points. </p>
  
  <p>I've thought about creating a start point and finding whether there exists a path that doesn't repeat points (ie (1,1) -> (2, 1) -> (1,1) disallowed) and could get back to the start point; however, if the start point is in an offshoot of the circle, this wouldn't work. </p>
  
  <p>For instance, a list of coordinates </p>
  
  <pre><code>[[0, 0], [0, 1], [1, 2], [2, 3], [3, 3], [3, 4], [4, 4], [3, 2], [3, 1], [3, 0], [2, -1], [1, -1], [0, -1]] 
  </code></pre>
  
  <p>would form a complete path while if I take out <code>[1, -1]</code> it would not form a complete path.</p>