FFT NTT 模板

NTT：

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 2000050
#define ll long long
#define MOD 998244353
template<typename T>
inline void read(T&x)
{
    T f=,c=;char ch=getchar();
    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}
    while(ch>=''&&ch<=''){c=*c+ch-'';ch=getchar();}
    x = f*c;
}
ll fastpow(ll x,int y)
{
    ll ret = ;
    while(y)
    {
        if(y&)ret=ret*x%MOD;
        x=x*x%MOD;
        y>>=;
    }
    return ret;
}
int n,m,mx,to[*N],lim=,l;
void ntt(ll *a,int len,int k)
{
    for(int i=;i<len;i++)
        if(i<to[i])swap(a[i],a[to[i]]);
    for(int i=;i<len;i<<=)
    {
        ll w0 = fastpow(,(MOD-)/(i<<));
        for(int j=;j<len;j+=(i<<))
        {
            ll w = ;
            for(int o=;o<i;o++,w=w*w0%MOD)
            {
                ll w1 = a[j+o],w2 = a[j+o+i]*w%MOD;
                a[j+o] = (w1+w2)%MOD;
                a[j+o+i] = ((w1-w2)%MOD+MOD)%MOD;
            }
        }
    }
    if(k==-)
        for(int i=;i<(lim>>);i++)swap(c[i],c[lim-i]);
}
ll a[*N],b[*N],c[*N];
int main()
{
    read(n),read(m);mx = max(n,m);
    for(int i=;i<=n;i++)read(a[i]);
    for(int i=;i<=m;i++)read(b[i]);
    while(lim<=*mx)lim<<=,l++;
    for(int i=;i<lim;i++)to[i]=((to[i>>]>>)|((i&)<<(l-)));
    ntt(a,lim,),ntt(b,lim,);
    for(int i=;i<lim;i++)c[i]=a[i]*b[i]%MOD;
    ntt(c,lim,-);
    ll inv = fastpow(lim,MOD-);
    for(int i=;i<lim;i++)c[i]=c[i]*inv%MOD;
    for(int i=;i<=n+m;i++)printf("%lld ",c[i]);
    puts("");
    return ;
}

FFT：

#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 2000050
#define ll long long
const double Pi = acos(-1.0);
template<typename T>
inline void read(T&x)
{
    T f=,c=;char ch=getchar();
    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}
    while(ch>=''&&ch<=''){c=*c+ch-'';ch=getchar();}
    x = f*c;
}
struct cp
{
    double x,y;
    cp(){}
    cp(double x,double y):x(x),y(y){}
};
cp operator + (cp &a,cp &b)
{
    return cp(a.x+b.x,a.y+b.y);
}
cp operator - (cp &a,cp &b)
{
    return cp(a.x-b.x,a.y-b.y);
}
cp operator * (cp &a,cp &b)
{
    return cp(a.x*b.x-a.y*b.y,a.x*b.y+a.y*b.x);
}
int n,m,mx,to[*N],lim=,l;
void fft(cp *a,int len,int k)
{
    for(int i=;i<len;i++)
        if(i<to[i])swap(a[i],a[to[i]]);
    for(int i=;i<len;i<<=)
    {
        cp w0(cos(Pi/i),k*sin(Pi/i));
        for(int j=;j<len;j+=(i<<))
        {
            cp w(,);
            for(int o=;o<i;o++,w=w*w0)
            {
                cp w1 = a[j+o],w2 = a[j+o+i]*w;
                a[j+o] = w1+w2;
                a[j+o+i] = w1-w2;
            }
        }
    }
}
cp a[*N],b[*N],c[*N];
int main()
{
    read(n),read(m);mx = max(n,m);
    for(int i=;i<=n;i++)read(a[i].x);
    for(int i=;i<=m;i++)read(b[i].x);
    while(lim<=*mx)lim<<=,l++;
    for(int i=;i<lim;i++)to[i]=((to[i>>]>>)|((i&)<<(l-)));
    fft(a,lim,),fft(b,lim,);
    for(int i=;i<lim;i++)c[i]=a[i]*b[i];
    fft(c,lim,-);
    for(int i=;i<=n+m;i++)
        printf("%lld ",(ll)(c[i].x/lim+0.5));
    puts("");
    return ;
}