What is the computational complexity of the n-dimensional FFT with m points along each dimension?
For a 1D FFT it's O(m log m).
For a 2D FFT you have to do m x 1D FFTs in each axis so that's O(2 m^2 log m) = O(m^2 log m).
It's too early in the morning here to get my head round n >= 3 but I'm guessing it's probably:
O(m^n log m)
来源：https://stackoverflow.com/questions/6514861/computational-complexity-of-the-fft-in-n-dimensions