3 2
11110001 11110001 11110000
11110000 11110000

If you alter one bit, it will become
11110000 11110000 11110001

So how the answer is 1 2? Shouldn't it be 1 1? Or we have to alter only the first byte?

What you suggest changes 2 bits and you want the replacement with minimal number of bits ("And if it is, find the minimum number of bits to alter.").
Edited by author 26.10.2013 17:33

Edited by author 26.10.2013 17:36

Use the FFTW.