mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
89 lines
1.8 KiB
C++
89 lines
1.8 KiB
C++
#include<iostream>
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#include<cstdio>
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#include<string.h>
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#include<algorithm>
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#include<complex>
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#define N 50010
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using namespace std;
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const double pi=acos(-1);
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const complex<double> I(0,1);
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const double eps=1e-6;
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char aa[N],bb[N];
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int ans[4*N];
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complex<double> a[4*N],b[4*N];
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int n;
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void initial()
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{
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int lenA=strlen(aa),lenB=strlen(bb);
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n=max(lenA,lenB);
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double t=log2(n);
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int tt=int(t);
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if(t-tt>0)tt++;
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n=1<<(tt+1);
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int i;
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for(i=0; i<lenA; i++)a[i]=aa[lenA-1-i]-'0';
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while(i<n)a[i++]=0;
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for(i=0; i<lenB; i++)b[i]=bb[lenB-1-i]-'0';
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while(i<n)b[i++]=0;
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}
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void bitReverse(complex<double> * a)
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{
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for(int i=1; i<n-1; i++)
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{
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int j=0;
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for(int k=1,tmp=i; k<n; j=((j<<1)|(tmp&1)),k<<=1,tmp>>=1);
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if(j>i)swap(a[i],a[j]);
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}
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}
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void iterative_FFT(complex<double> *a,int sig)
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{
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bitReverse(a);
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for(int m=2; m<=n; m<<=1)
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{
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int mh =m>>1;
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for(int i=0; i<mh; i++)
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{
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complex<double> wi=exp(i*sig*pi/mh*I);
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for(int j=i; j<n; j+=m)
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{
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int k=j+mh;
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complex<double> u=a[j],t=wi*a[k];;
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a[j]=u+t;
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a[k]=u-t;
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}
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}
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}
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if(sig==-1)for(int i=0; i<n; i++)a[i]/=n;
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}
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void convolution()
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{
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iterative_FFT(a,1);
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iterative_FFT(b,1);
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for(int i=0; i<n; i++)a[i]*=b[i];
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iterative_FFT(a,-1);
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}
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void output()
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{
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int k=0;
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ans[0]=0;
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for(int i=0; i<n; i++)
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{
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int tmp=a[i].real()+eps;
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ans[i]+=tmp;
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if(ans[i])k=i,ans[i+1]=ans[i]/10,ans[i]%=10;
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else ans[i+1]=0;
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}
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while(k>=0)cout<<ans[k--];
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cout<<endl;
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}
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int main()
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{
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while(~scanf("%s%s",aa,bb))
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{
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initial();
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convolution();
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output();
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}
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return 0;
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}
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