89 lines
1.8 KiB
C++
89 lines
1.8 KiB
C++
#include<iostream>
|
|
#include<cstdio>
|
|
#include<string.h>
|
|
#include<algorithm>
|
|
#include<complex>
|
|
#define N 50010
|
|
using namespace std;
|
|
const double pi=acos(-1);
|
|
const complex<double> I(0,1);
|
|
const double eps=1e-6;
|
|
char aa[N],bb[N];
|
|
int ans[4*N];
|
|
complex<double> a[4*N],b[4*N];
|
|
int n;
|
|
void initial()
|
|
{
|
|
int lenA=strlen(aa),lenB=strlen(bb);
|
|
n=max(lenA,lenB);
|
|
double t=log2(n);
|
|
int tt=int(t);
|
|
if(t-tt>0)tt++;
|
|
n=1<<(tt+1);
|
|
int i;
|
|
for(i=0; i<lenA; i++)a[i]=aa[lenA-1-i]-'0';
|
|
while(i<n)a[i++]=0;
|
|
for(i=0; i<lenB; i++)b[i]=bb[lenB-1-i]-'0';
|
|
while(i<n)b[i++]=0;
|
|
}
|
|
void bitReverse(complex<double> * a)
|
|
{
|
|
for(int i=1; i<n-1; i++)
|
|
{
|
|
int j=0;
|
|
for(int k=1,tmp=i; k<n; j=((j<<1)|(tmp&1)),k<<=1,tmp>>=1);
|
|
if(j>i)swap(a[i],a[j]);
|
|
}
|
|
}
|
|
void iterative_FFT(complex<double> *a,int sig)
|
|
{
|
|
bitReverse(a);
|
|
for(int m=2; m<=n; m<<=1)
|
|
{
|
|
int mh =m>>1;
|
|
for(int i=0; i<mh; i++)
|
|
{
|
|
complex<double> wi=exp(i*sig*pi/mh*I);
|
|
for(int j=i; j<n; j+=m)
|
|
{
|
|
int k=j+mh;
|
|
complex<double> u=a[j],t=wi*a[k];;
|
|
a[j]=u+t;
|
|
a[k]=u-t;
|
|
}
|
|
}
|
|
}
|
|
if(sig==-1)for(int i=0; i<n; i++)a[i]/=n;
|
|
}
|
|
void convolution()
|
|
{
|
|
iterative_FFT(a,1);
|
|
iterative_FFT(b,1);
|
|
for(int i=0; i<n; i++)a[i]*=b[i];
|
|
iterative_FFT(a,-1);
|
|
}
|
|
void output()
|
|
{
|
|
int k=0;
|
|
ans[0]=0;
|
|
for(int i=0; i<n; i++)
|
|
{
|
|
int tmp=a[i].real()+eps;
|
|
ans[i]+=tmp;
|
|
if(ans[i])k=i,ans[i+1]=ans[i]/10,ans[i]%=10;
|
|
else ans[i+1]=0;
|
|
}
|
|
while(k>=0)cout<<ans[k--];
|
|
cout<<endl;
|
|
}
|
|
int main()
|
|
{
|
|
while(~scanf("%s%s",aa,bb))
|
|
{
|
|
initial();
|
|
convolution();
|
|
output();
|
|
}
|
|
return 0;
|
|
}
|