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=270010;
const double pi=acos(-1.0),eps=1e-4;
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=1;
int main(){
    scanf("%d%d",&n,&m);
    n++;m++;
    while(N<n+m)N<<=1;
    for(int i=0;i<n;i++)scanf("%lf",&A[i].a);
    for(int i=0;i<m;i++)scanf("%lf",&B[i].a);
    FFT(A,N,1);
    FFT(B,N,1);
    for(int i=0;i<N;i++)A[i]=A[i]*B[i];
    FFT(A,N,-1);
    for(int i=0;i<n+m-1;i++)printf("%d ",(int)(A[i].a+eps));
    return 0;
}
void FFT(Complex *A,int n,int tp){
    for(int i=1,j=0;i<n-1;i++){
        int k=N;
        do{
            k>>=1;
            j^=k;
        }while(j<k);
        if(i<j)swap(A[i],A[j]);
    }
    for(int k=2;k<=n;k<<=1){
        Complex wn(cos(-tp*2*pi/k),sin(-tp*2*pi/k));
        for(int i=0;i<n;i+=k){
            Complex w(1.0,0.0);
            for(int j=0;j<(k>>1);j++,w=w*wn){
                Complex a(A[i+j]),b(w*A[i+j+(k>>1)]);
                A[i+j]=a+b;
                A[i+j+(k>>1)]=a-b;
            }
        }
    }
    if(tp<0)for(int i=0;i<n;i++)A[i].a/=n;
}

挖个大坑：

COGS2216 你猜是不是KMP