51nod1565 FFT

思路：

显然拆位FFT 不解释

//By SiriusRen
#include <bits/stdc++.h>
using namespace std;
const int N=;
const double pi=acos(-);
int n=,L,S,T,k,sa[N],st[N],sc[N],sg[N],R[N],csa,cst,csc,csg,ans;
char s[N],t[N],A[N];
struct Complex{double x,y;Complex(){}Complex(double X,double Y){x=X,y=Y;}}Sa[N],St[N],Sc[N],Sg[N],Ta[N],Tt[N],Tc[N],Tg[N];
Complex operator+(Complex a,Complex b){return Complex(a.x+b.x,a.y+b.y);}
Complex operator-(Complex a,Complex b){return Complex(a.x-b.x,a.y-b.y);}
Complex operator*(Complex a,Complex b){return Complex(a.x*b.x-a.y*b.y,a.x*b.y+a.y*b.x);}
Complex operator/(Complex a,int b){return Complex(a.x/b,a.y/b);}
void FFT(Complex *a,int f){
    for(int i=;i<n;i++)if(i<R[i])swap(a[i],a[R[i]]);
    for(int l=;l<n;l<<=){
        Complex wn=Complex(cos(pi/l),f*sin(pi/l));
        for(int j=;j<n;j+=(l<<)){
            Complex w=Complex(,);
            for(int k=;k<l;k++,w=w*wn){
                Complex X=a[j+k],Y=w*a[j+k+l];
                a[j+k]=X+Y,a[j+k+l]=X-Y;
            }
        }
    }if(f==-)for(int i=;i<n;i++)a[i]=a[i]/n;
}
int main(){
    scanf("%d%d%d%s%s",&S,&T,&k,s+,t+);
    for(;n<=S+T;n<<=)L++;
    for(int i=;i<n;i++)R[i]=(R[i>>]>>)|((i&)<<(L-));
    for(int i=;i<=S;i++){
        if(s[i]=='A')sa[max(,i-k)]++,sa[i+k+]--;
        else if(s[i]=='T')st[max(,i-k)]++,st[i+k+]--;
        else if(s[i]=='C')sc[max(,i-k)]++,sc[i+k+]--;
        else if(s[i]=='G')sg[max(,i-k)]++,sg[i+k+]--;
    }
    for(int i=;i<=S;i++)sa[i]+=sa[i-],st[i]+=st[i-],sc[i]+=sc[i-],sg[i]+=sg[i-];
    for(int i=;i<=T;i++){
        if(t[i]=='A')Ta[T-i]=Complex(,),csa++;
        else if(t[i]=='T')Tt[T-i]=Complex(,),cst++;
        else if(t[i]=='C')Tc[T-i]=Complex(,),csc++;
        else if(t[i]=='G')Tg[T-i]=Complex(,),csg++;
    }
    for(int i=;i<=S;i++){
        if(sa[i])Sa[i-]=Complex(,);
        if(st[i])St[i-]=Complex(,);
        if(sc[i])Sc[i-]=Complex(,);
        if(sg[i])Sg[i-]=Complex(,);
    }
    FFT(Sa,),FFT(St,),FFT(Sc,),FFT(Sg,),FFT(Ta,),FFT(Tt,),FFT(Tc,),FFT(Tg,);
    for(int i=;i<n;i++)Sa[i]=Sa[i]*Ta[i];
    for(int i=;i<n;i++)St[i]=St[i]*Tt[i];
    for(int i=;i<n;i++)Sc[i]=Sc[i]*Tc[i];
    for(int i=;i<n;i++)Sg[i]=Sg[i]*Tg[i];
    FFT(Sa,-),FFT(St,-),FFT(Sc,-),FFT(Sg,-);
    for(int i=;i<S;i++)A[i]=;
    for(int i=;i<S;i++)
        if((int)(Sa[i+T-].x+0.2)!=csa||(int)(St[i+T-].x+0.2)!=cst||(int)(Sc[i+T-].x+0.2)!=csc||(int)(Sg[i+T-].x+0.2)!=csg)A[i]=;
    for(int i=;i<S;i++)if(A[i])ans++;
    printf("%d\n",ans);
}