title: Determine the unique string from a repeating string in C#
body: <p>I need to develop an efficient algorithm for determining the unique (repeated) string given a string with repeating content (and only repeating content)...</p>
  
  <p>For example:</p>
  
  <p><code>"AbcdAbcdAbcdAbcd"</code> => <code>"Abcd"</code></p>
  
  <p><code>"Hello"</code> => <code>"Hello"</code></p>
  
  <p>I'm having some trouble coming up with an algorithm that is fairly efficient; any input would be appreciated.</p>
  
  <p>Clarification: I want <strong>the shortest string that, when repeated enough times, is equal to the total string</strong>.</p>