FFT板子

woc......FFT这玩意儿真坑......

一上午除了打了几遍板子什么也没干......真是废了......

你要加油啊......

 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<algorithm>
 using namespace std;
 const int maxn=;
 const double pi=acos(-1.0),eps=1e-;
 struct Complex{
     double a,b;
     Complex(double a=0.0,double b=0.0):a(a),b(b){}
     Complex operator+(const Complex &x)const{return Complex(a+x.a,b+x.b);}
     Complex operator-(const Complex &x)const{return Complex(a-x.a,b-x.b);}
     Complex operator*(const Complex &x)const{return Complex(a*x.a-b*x.b,a*x.b+b*x.a);}
 }A[maxn],B[maxn];
 void FFT(Complex*,int,int);
 int n,m,N=;
 int main(){
     scanf("%d%d",&n,&m);
     n++;m++;
     while(N<n+m)N<<=;
     for(int i=;i<n;i++)scanf("%lf",&A[i].a);
     for(int i=;i<m;i++)scanf("%lf",&B[i].a);
     FFT(A,N,);
     FFT(B,N,);
     for(int i=;i<N;i++)A[i]=A[i]*B[i];
     FFT(A,N,-);
     for(int i=;i<n+m-;i++)printf("%d ",(int)(A[i].a+eps));
     return ;
 }
 void FFT(Complex *A,int n,int tp){
     for(int i=,j=;i<n-;i++){
         int k=N;
         do{
             k>>=;
             j^=k;
         }while(j<k);
         if(i<j)swap(A[i],A[j]);
     }
     for(int k=;k<=n;k<<=){
         Complex wn(cos(-tp**pi/k),sin(-tp**pi/k));
         for(int i=;i<n;i+=k){
             Complex w(1.0,0.0);
             for(int j=;j<(k>>);j++,w=w*wn){
                 Complex a(A[i+j]),b(w*A[i+j+(k>>)]);
                 A[i+j]=a+b;
                 A[i+j+(k>>)]=a-b;
             }
         }
     }
     if(tp<)for(int i=;i<n;i++)A[i].a/=n;
 }

挖个大坑：

COGS2216 你猜是不是KMP