BZOJ 2194 fast Fourier-Fast Fourier Transformation

BZOJ 2194 fast Fourier-Fast Fourier Transformation

Given two sequences a and B with a length of n, evaluate c [k] = Σ a [I] * B [I-k].

This is not a convolution form, so we reverse the B array, followed by the convolution form.

Then♂Happy ground FFT

 

#include 
 
  #include 
  
   #include 
   
    #include 
    
     #include #define M 263000#define PI 3.1415926535897932384626433832795028841971using namespace std;struct Complex{double a,b;Complex() {}Complex(double _,double __):a(_),b(__) {}Complex operator + (const Complex &x) const{return Complex(a+x.a,b+x.b);}Complex operator - (const Complex &x) const{return Complex(a-x.a,b-x.b);}Complex operator * (const Complex &x) const{return Complex(a*x.a-b*x.b,a*x.b+b*x.a);}void operator *= (const Complex &x){*this=(*this)*x;}}a[M],b[M],p[M];int n;void FFT(Complex x[],int n,int type){static Complex temp[M];if(n==1) return ;int i;for(i=0;i
     
      >1]=x[i],temp[i+n>>1]=x[i+1];memcpy(x,temp,sizeof(Complex)*n);Complex *l=x,*r=x+(n>>1);FFT(l,n>>1,type);FFT(r,n>>1,type);Complex root(cos(type*2*PI/n),sin(type*2*PI/n)),w(1,0);for(i=0;i
      
       >1;i++,w*=root)temp[i]=l[i]+w*r[i],temp[i+(n>>1)]=l[i]-w*r[i];memcpy(x,temp,sizeof(Complex)*n);}int main(){int i,digit;cin>>n;for(i=0;i