Looks like the algorithms used for detecting plagiatism could help you here. If you are able to understand german, the following link to the Bauhaus University Weimar may help you: Search for documents on plagiatism-detection (most in german). In 2009 the university held a competition which sounds similar to your use-case

HTH, Rata

In reply to Re: general advice finding duplicate code by Ratazong
in thread general advice finding duplicate code by aquarium

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