I wrote a research paper and just realized that my idea has been published before. Must I cite?
Must I cite?


Yes, you must cite the thesis, since it's part of an author's responsibility to give an accurate representation of the state of the art.


  I understand now that I can no longer publish my technique


I think these worries might be unjustified. Most research is incremental, in the sense that it improves on existing work, rather than inventing something completely new. Just cite the work and clearly discuss (or even better, show experimental evidence) why your technique gives an improvement in terms of generality and speed.