title: Duplicate substring searching
body: <p>Is there any efficient way to find the duplicate substring? Here, duplicate means that two same substring close to each other have the same value without overlap. For example, the source string is:</p>
  
  <pre><code>ABCDDEFGHFGH
  </code></pre>
  
  <p>'D' and 'FGH' is duplicated. 'F' appear two times in the sequence, however, they are not close to each other, so it does not duplicate. so our algorithm will return ['D', 'FGH']. I want to know whether there exists an elegant algorithm instead the brute force method?</p>