Iterative from Recursive [Answered]

int ii = 0;
            int kk = 0;
            int N = x.Length;

            Complex[] Y = new Complex[N];


            if (N == 1)
            {
                Y[0] = x[0];
                return Y;
            }

            Complex[] E, O, even, odd = new Complex[N / 2];
            E = O = even = odd;

            for (ii = 0; ii < N; ii++)
            {

                if (ii % 2 == 0)
                {
                    even[ii / 2] = x[ii];
                }
                if (ii % 2 == 1)
                {
                    odd[(ii - 1) / 2] = x[ii];
                }
            }

            E = fft(even);
            O = fft(odd);

            for (kk = 0; kk < N; kk++)
            {
                Y[kk] = E[(kk % (N / 2))] + O[(kk % (N / 2))] * twiddles[kk * wSamp / N];
            }

            return Y;