FFT 模板

#include<bits/stdc++.h>
#define ll long long
#define N 600005
using namespace std;
inline int read(){
  int x=,f=;char ch=getchar();
  while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}
  while(ch>=''&&ch<=''){x=*x+ch-'';ch=getchar();}
  return x*f;
}
struct CD{
  double x,y;
  CD(double a=,double b=){x=a,y=b;}
  friend CD operator + (CD n1,CD n2){return CD(n1.x+n2.x,n1.y+n2.y);}
  friend CD operator - (CD n1,CD n2){return CD(n1.x-n2.x,n1.y-n2.y);}
  friend CD operator * (CD n1,CD n2){return CD(n1.x*n2.x-n1.y*n2.y,n1.x*n2.y+n1.y*n2.x);}
};
const double Pi=acos(-1.0);
int bit,n,m,nn;
CD a[N],b[N];
void FFT(CD *a,int n,int type){
  for(int i=,j=;i<n;i++) {
    if(j>i)swap(a[i],a[j]);
    int k=n;
    while(j&(k >>= ))j&=~k;
    j|=k;
  }
  for(int i=;i<=bit;i++){
    CD w_n(cos(*type*Pi/(<<i)),sin(*type*Pi/(<<i)));
    for(int j=;j<n;j+=(<<i)){
      CD w(,);
      for(int k=j;k<j+(<<(i-));k++){
        CD tmp=a[k],tt=w*a[k+(<<(i-))];
        a[k]=tmp+tt;
        a[k+(<<(i-))]=tmp-tt;
        w=w*w_n;
      }
    }
  }
  if(type<)for(int i=;i<n;i++)a[i].x/=n;
}
int main(){
  n=read();m=read();n++;m++;
  for(int i=;i<n;i++)scanf("%lf",&a[i].x),a[i].y=0.0;
  for(int i=;i<m;i++)scanf("%lf",&b[i].x),b[i].y=0.0;
  bit=;
  while((<<bit)<(n+m-))bit++;
  nn=<<bit;
  for(int i=n;i<nn;i++)a[i]=CD(0.0,0.0);
  for(int i=m;i<nn;i++)b[i]=CD(0.0,0.0);
 
  FFT(a,nn,);FFT(b,nn,);
  for(int i=;i<nn;i++)a[i]=a[i]*b[i];
  FFT(a,nn,-);
 
  for(int i=;i<(n+m-);i++)printf("%d ",(int)(a[i].x+0.5));
  return ;
}