【BZOJ】3527: [Zjoi2014]力

题目链接：http://www.lydsy.com/JudgeOnline/problem.php?id=3527

把${f_i}$消去之后换元就是卷积的形式，直接算就可以了。

---

 #include<iostream>
 #include<cstdio>
 #include<algorithm>
 #include<vector>
 #include<cstdlib>
 #include<cmath>
 #include<complex>
 #include<cstring>
 using namespace std;
 #define maxn 1001000
 #define llg long long
 #define Pi acos(-1.0)
 #define yyj(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
 typedef complex<double> XU;

 struct FFT
 {
     llg rev[maxn],L,n;
     double c[maxn];
     void fft(XU *z,llg f)
     {
         for (llg i=;i<n;i++) if (i<rev[i]) swap(z[i],z[rev[i]]);
         for (llg i=;i<n;i*=)
         {
             XU wn(cos(Pi/i),sin(Pi/i));
             for (llg p=i*,j=;j<n;j+=p)
             {
                 XU w(,);
                 for (llg k=;k<i;k++,w*=wn)
                 {
                     XU x=z[j+k],y=z[j+k+i]*w;
                     z[j+k]=x+y,z[j+k+i]=x-y;
                 }
             }
         }
         if (f==-) reverse(z+,z+n);
     }

     XU a[maxn],b[maxn];

     void work()
     {
         llg m=(n-)*;
         for (n=;n<=m;n*=) L++;
         for (llg i=;i<n;i++) rev[i]=(rev[i/]/)|((i&)<<(L-));
         fft(a,),fft(b,);
         for (llg i=;i<n;i++) a[i]*=b[i];
         fft(a,-);
         for (llg i=;i<n;i++) c[i]=(a[i].real()/n);
     }
 }F1,F2;

 double x[maxn];

 int main()
 {
     yyj("li");
     llg N;
     cin>>N;
     F1.n=N;
     for (llg i=;i<N;i++) scanf("%lf",&x[i]),F1.a[i]=x[i];
     for (llg i=;i<=N-;i++) F1.b[i]=(double)-1.0/(double)(N--i)/(double)(N--i);
     for (llg i=N;i<=*N-;i++) F1.b[i]=(double)1.0/(double)(N--i)/(double)(N--i);
     F1.work();
     for (llg i=N-;i<*N-;i++) printf("%.9lf\n",F1.c[i]) ;
     return ;
 }