代码

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<algorithm>
#define N (5000000+100)
using namespace std;

double pi=acos(-1.0);
int n,m,fn,l,r[N];
struct complex
{
    double x,y;
    complex (double xx=0,double yy=0)
    {
        x=xx; y=yy;
    }
}a[N],b[N];

complex operator + (complex a,complex b){return complex(a.x+b.x,a.y+b.y);}
complex operator - (complex a,complex b){return complex(a.x-b.x,a.y-b.y);}
complex operator * (complex a,complex b){return complex(a.x*b.x-a.y*b.y,a.x*b.y+a.y*b.x);}
complex operator / (complex a,double b){return complex(a.x/b,a.y/b);}

void FFT(int n,complex *a,int opt)
{
    for (int i=0; i<n; ++i)
        if (i<r[i])
            swap(a[i],a[r[i]]);
    for (int k=1; k<n; k<<=1)
    {
        complex wn=complex(cos(pi/k),opt*sin(pi/k));
        for (int i=0; i<n; i+=(k<<1))
        {
            complex w=complex(1,0);
            for (int j=0; j<k; ++j,w=w*wn)
            {
                complex x=a[i+j], y=w*a[i+j+k];
                a[i+j]=x+y; a[i+j+k]=x-y;
            }
        }
    }
    if (opt==-1) for (int i=0; i<n; ++i) a[i]=a[i]/n;
}

int main()
{
    scanf("%d%d",&n,&m);
    for (int i=0; i<=n; ++i)
        scanf("%lf",&a[i].x);
    for (int i=0; i<=m; ++i)
        scanf("%lf",&b[i].x);
    
    fn=1;
    while (fn<=n+m) fn<<=1, l++;
    for (int i=0; i<fn; ++i)
        r[i]=(r[i>>1]>>1) | ((i&1)<<(l-1));
        
    FFT(fn,a,1); FFT(fn,b,1);
    for (int i=0; i<=fn; ++i)
        a[i]=a[i]*b[i];
    FFT(fn,a,-1);
    
    for (int i=0; i<=n+m; ++i)
        printf("%d ",(int)(a[i].x+0.5));
}

评测结果