static ulong[] InverseFft(ulong[] vector)
{
var size = vector.Length;
if (size == 1)
{
return(vector);
}
var evenVector = new ulong[size / 2];
var oddVector = new ulong[size / 2];
for (int i = 0; i < size / 2; i++)
{
evenVector[i] = vector[2 * i];
oddVector[i] = vector[2 * i + 1];
}
evenVector = InverseFft(evenVector);
oddVector = InverseFft(oddVector);
ulong pow = (ulong)(Power / size);
ulong root_n = IntegerMath.ModPow(Root_1, pow, Mod);
ulong w = 1;
var result = new ulong[size];
for (int i = 0; i < size / 2; i++)
{
result[i] = (Inverse * (evenVector[i] + (w * oddVector[i]) % Mod) % Mod) % Mod;
result[i + size / 2] =
(Inverse * (evenVector[i] + Mod - (w * oddVector[i]) % Mod) % Mod) % Mod;
w = (root_n * w) % Mod;
}
return(result);
}
static ulong[] SlowInverseFt(ulong[] vector)
{
var size = vector.Length;
var res = new ulong[size];
ulong pow = (ulong)(Power / size);
ulong root_n = IntegerMath.ModPow(Root_1, pow, Mod);
ulong root_i = 1;
for (int i = 0; i < size; i++)
{
double temp = 0;
ulong root_j = 1;
for (int j = 0; j < size; j++)
{
temp = (temp + (vector[j] * root_j) % Mod) % Mod;
root_j = (root_j * root_i) % Mod;
}
res[i] = (ulong)(temp * IntegerMath.Inverse((ulong)size, Mod)) % Mod;
root_i = (root_i * root_n) % Mod;
}
return(res);
}
