UOJ 34 多项式乘法

刷了一遍FFT

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

struct Complex
{
double real,i;
Complex (double a=0,double b=0) {real=a;i=b;}
Complex operator + (Complex that) {return Complex(real+that.real,i+that.i);}
Complex operator - (Complex that) {return Complex(real-that.real,i-that.i);}
Complex operator * (Complex that) {return Complex(real*that.real-i*that.i,real*that.i+i*that.real);}
};/*
struct Complex
{
double real,i;
Complex(double a=0,double b=0){real=a,i=b;}
Complex operator + (Complex a){return Complex(real+a.real,i+a.i);}
Complex operator - (Complex a){return Complex(real-a.real,i-a.i);}
Complex operator * (Complex a){return Complex(real*a.real-i*a.i,i*a.real+real*a.i);}
}; */
const double PI = acos(-1);
const int MAXN = 3e5+10;

int n,m,nm;
Complex a[MAXN],b[MAXN];
int rev[MAXN];
void FFT(Complex a[],int type)
{
for(int i=0;i<nm;i++) if(rev[i]<i) swap(a[i],a[rev[i]]);
for(int i=2;i<=nm;i<<=1)
{
Complex wn(cos(2*PI/i),type*sin(2*PI/i));
for(int j=0;j<nm;j+=i)
{
Complex t,tmp,w(1,0);
for(int k=0;k<i/2;k++)
{
t=a[j+k+i/2]*w;
a[j+k+i/2]=a[j+k]-t;
a[j+k]=a[j+k]+t;
w=w*wn;
}
}
}
/*int n=nm;
for(int i=0;i<n;i++) if(rev[i]<i) swap(a[i],a[rev[i]]);
// for(int i=0;i<n;i++) cout<<x[i]<<' ';cout<<endl;
for(int i=2;i<=n;i*=2)
{
Complex wn(cos(2*PI/i),type*sin(2*PI/i));
// cout<<wn<<endl;
for(int j=0;j<n;j+=i)
{
Complex w(1,0),t,tmp;
for(int k=0;k<i/2;k++)
{
tmp=a[j+k];
t=a[j+k+i/2]*w;
a[j+k]=tmp+t;
a[j+k+i/2]=tmp-t;
w=w*wn;
}
}
}*/
}

int main()
{
cin >>n >>m;
n++;m++;
for(int i=0;i<n;i++) scanf("%lf",&a[i].real);
for(int i=0;i<m;i++) scanf("%lf",&b[i].real);
int cnt=1;nm=1;
while(nm<n+m+1) nm<<=1,cnt++;cnt-=2;//cout<<((3&1)<<cnt)<<endl;
for(int i=0;i<nm;i++) rev[i]=(rev[i>>1]>>1)|((i&1)<<cnt);//,cout<<rev[i]<<' ';
FFT(a,1);FFT(b,1);
for(int i=0;i<nm;i++) a[i]=a[i]*b[i];
FFT(a,-1);
for(int i=0;i<n+m-1;i++) printf("%d ",(int)(a[i].real/nm+0.5));
return 0;
}