BZOJ4133 : Answer的排队

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
const int N=65555,M=32768,P=1000000007;
int n,m,i,j,k,t,o,len,L,R,a[30],b[N],f[N*3],ans,g[N],v[N],fin[N],fac[N],inv[N],pos[N];
inline void up(int&a,int b){(a+=b)>=P&&(a-=P);}
inline int C(int n,int m){return 1LL*fac[n]*inv[m]%P*inv[n-m]%P;}
namespace FFT{
struct comp{
  long double r,i;comp(long double _r=0,long double _i=0){r=_r;i=_i;}
  comp operator+(const comp&x){return comp(r+x.r,i+x.i);}
  comp operator-(const comp&x){return comp(r-x.r,i-x.i);}
  comp operator*(const comp&x){return comp(r*x.r-i*x.i,r*x.i+i*x.r);}
  comp conj(){return comp(r,-i);}
}A[N],B[N];
int a0[N],b0[N],a1[N],b1[N];
const long double pi=acos(-1.0);
void FFT(comp a[],int n,int t){
  for(int i=1;i<n;i++)if(i<pos[i])swap(a[i],a[pos[i]]);
  for(int d=0;(1<<d)<n;d++){
    int m=1<<d,m2=m<<1;
    long double o=pi*2/m2*t;comp _w(cos(o),sin(o));
    for(int i=0;i<n;i+=m2){
      comp w(1,0);
      for(int j=0;j<m;j++){
        comp&A=a[i+j+m],&B=a[i+j],t=w*A;
        A=B-t;B=B+t;w=w*_w;
      }
    }
  }
  if(t==-1)for(int i=0;i<n;i++)a[i].r/=n;
}
void mul(int*a,int*b,int*c,int k){
  int i,j;
  for(i=0;i<k;i++)A[i]=comp(a[i],b[i]);
  FFT(A,k,1);
  for(i=0;i<k;i++){
    j=(k-i)&(k-1);
    B[i]=(A[i]*A[i]-(A[j]*A[j]).conj())*comp(0,-0.25);
  }
  FFT(B,k,-1);
  for(i=0;i<k;i++)c[i]=((long long)(B[i].r+0.5))%P;
}
void mulmod(int*a,int*b,int*c,int k){
  int i;
  for(i=0;i<k;i++)a0[i]=a[i]/M,b0[i]=b[i]/M;
  for(mul(a0,b0,a0,k),i=0;i<k;i++){
    c[i]=1LL*a0[i]*M*M%P;
    a1[i]=a[i]%M,b1[i]=b[i]%M;
  }
  for(mul(a1,b1,a1,k),i=0;i<k;i++){
    c[i]=(a1[i]+c[i])%P,a0[i]=(a0[i]+a1[i])%P;
    a1[i]=a[i]/M+a[i]%M,b1[i]=b[i]/M+b[i]%M;
  }
  for(mul(a1,b1,a1,k),i=0;i<k;i++)c[i]=(1LL*M*(a1[i]-a0[i]+P)+c[i])%P;
}
}
inline void solve(int len,int K){
  int i,j,k;
  for(k=1;k<=len;k<<=1);k<<=1;
  j=__builtin_ctz(k)-1;
  for(i=0;i<k;i++)pos[i]=pos[i>>1]>>1|((i&1)<<j);
  for(i=0;i<=len;i++)v[i]=C(i+K-1,K-1);
  for(g[0]=0;i<k;i++)v[i]=g[i]=0;
  FFT::mulmod(g,v,fin,k);
  for(i=1;i<=len;i++)g[i]=fin[i];
}
int main(){
  scanf("%d%d",&n,&m);
  for(fac[0]=i=1;i<=n*2;i++)fac[i]=1LL*fac[i-1]*i%P;
  for(inv[0]=inv[1]=1,i=2;i<=n*2;i++)inv[i]=1LL*(P-P/i)*inv[P%i]%P;
  for(i=2;i<=n*2;i++)inv[i]=1LL*inv[i-1]*inv[i]%P;
  for(i=1;i<=m;i++)scanf("%d",&a[i]);
  for(i=1;i<m;i++)for(j=a[i];j<a[i+1];j++)b[j]=i&1;
  for(i=a[2],L=1+N,f[R=i+N]=1;i<n;i=j){
    for(j=i;j<n&&b[i]==b[j];j++);
    t=j-i;
    for(k=L;k<=R;k++)g[k-L+1]=f[k];
    len=R-L+1;
    if(!b[i])reverse(g+1,g+len+1);
    solve(len,t);
    if(!b[i])reverse(g+1,g+len+1);
    for(k=L;k<=R;k++)f[k]=g[k-L+1];
    b[i]?L-=t:R+=t;
  }
  for(i=L;i<=R;i++)up(ans,f[i]);
  return printf("%d",ans),0;
}