FFT 模板

#include<bits/stdc++.h>
#define ll long long
#define N 600005
using namespace std;
inline int read(){
int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=10*x+ch-'0';ch=getchar();}
return x*f;
}
struct CD{
double x,y;
CD(double a=0,double b=0){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
,b
;
void FFT(CD *a,int n,int type){
for(int i=0,j=0;i<n;i++) {
if(j>i)swap(a[i],a[j]);
int k=n;
while(j&(k >>= 1))j&=~k;
j|=k;
}
for(int i=1;i<=bit;i++){
CD w_n(cos(2*type*Pi/(1<<i)),sin(2*type*Pi/(1<<i)));
for(int j=0;j<n;j+=(1<<i)){
CD w(1,0);
for(int k=j;k<j+(1<<(i-1));k++){
CD tmp=a[k],tt=w*a[k+(1<<(i-1))];
a[k]=tmp+tt;
a[k+(1<<(i-1))]=tmp-tt;
w=w*w_n;
}
}
}
if(type<0)for(int i=0;i<n;i++)a[i].x/=n;
}
int main(){
n=read();m=read();n++;m++;
for(int i=0;i<n;i++)scanf("%lf",&a[i].x),a[i].y=0.0;
for(int i=0;i<m;i++)scanf("%lf",&b[i].x),b[i].y=0.0;
bit=1;
while((1<<bit)<(n+m-1))bit++;
nn=1<<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,1);FFT(b,nn,1);
for(int i=0;i<nn;i++)a[i]=a[i]*b[i];
FFT(a,nn,-1);

for(int i=0;i<(n+m-1);i++)printf("%d ",(int)(a[i].x+0.5));
return 0;
}