[poj2389]Bull Math
再次练习FFT模板。。。
1 #include <iostream> 2 #include <algorithm> 3 #include <cstdio> 4 #include <cstring> 5 #include <cstdlib> 6 #include <complex> 7 using namespace std; 8 const int N=100000; 9 typedef complex<double> c; 10 char a[N],b[N]; 11 c F[N*2],A[N*2],B[N*2]; 12 int ans[N*2]; 13 14 int rev(int x,int n){ 15 int ret=0; 16 for(int i=0;(1<<i)<n;i++)ret=(ret<<1)|((x&(1<<i))>0); 17 return ret; 18 } 19 20 void fft(c *a,int n,int f){ 21 for(int i=0;i<n;i++)F[rev(i,n)]=a[i]; 22 for(int i=2;i<=n;i<<=1){ 23 c wn=c(cos(2*acos(-1)*f/i),sin(2*acos(-1)*f/i)); 24 for(int j=0;j<n;j+=i){ 25 c w=1; 26 for(int k=j;k<j+i/2;k++){ 27 c u=F[k],t=w*F[k+i/2]; 28 F[k]=u+t,F[k+i/2]=u-t,w*=wn; 29 } 30 } 31 } 32 for(int i=0;i<n;i++)a[i]=F[i]/=(f==-1?n:1); 33 } 34 35 int main(){ 36 scanf("%s%s",a,b); 37 int len1=strlen(a),len2=strlen(b),n1=1,n2=1,n=1; 38 while(n1<=len1)n1<<=1; 39 while(n2<=len2)n2<<=1; 40 while(n<2*max(n1,n2))n<<=1; 41 for(int i=0;i<n;i++)A[i]=(i<len1?a[len1-i-1]-'0':0); 42 for(int i=0;i<n;i++)B[i]=(i<len2?b[len2-i-1]-'0':0); 43 fft(A,n,1); 44 fft(B,n,1); 45 for(int i=0;i<n;i++)A[i]*=B[i]; 46 fft(A,n,-1); 47 for(int i=0;i<n;i++)ans[i]=int(A[i].real()+0.5); 48 for(int i=0;i<n-1;i++)ans[i+1]+=ans[i]/10,ans[i]%=10; 49 bool f=0; 50 for(int i=n-1;i>=0;i--)ans[i]?printf("%d",ans[i]),f=1:f||!i?printf("0"):0; 51 }
