Please can you help me with my problem? On Wikipedia, in article Discrete sine transform, this is written (chapter Computation):  

"*Although the direct application of these formulas would require O(N2) operations, it is possible to compute the same thing with only O(N log N) complexity by factorizing the computation similar to the fast Fourier transform (FFT). (**One can also compute DSTs via FFTs combined with O(N) pre- and post-processing steps.**)*"