bzoj3527 -- FFT

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代码：
 1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cmath> 5 #include<algorithm> 6 using namespace std; 7 #define N 800010 8 #define PI acos(-1.0) 9 struct E{10     double r,i;11     E(){}12     E(double r,double i):r(r),i(i){}13     void operator /= (double a){r/=a;i/=a;}14     E operator + (E a){return E(r+a.r,i+a.i);}15     E operator - (E a){return E(r-a.r,i-a.i);}16     E operator * (E a){return E(r*a.r-i*a.i,r*a.i+i*a.r);}17 }a[N],b[N],c[N];18 int i,j,k,n,m,M,r[N],l;19 double p[N],q[N];20 inline void FFT(E* a,int n,int d){21     for(int i=0;i<n;i++)if(r[i]>i)swap(a[i],a[r[i]]);22     for(int i=1;i<n;i<<=1){23         E wn(cos(PI/i),d*sin(PI/i));24         for(int j=0;j<n;j+=i<<1){25             E w(1,0);26             for(int k=0;k<i;k++){27                 E x=a[j+k],y=a[j+k+i]*w;28                 a[j+k]=x+y;a[j+k+i]=x-y;29                 w=w*wn;30             }31         }32     }33     if(d==-1)for(int i=0;i<n;i++)a[i]/=n;34 }35 int main()36 {37     scanf("%d",&n);38     for(i=1;i<=n;i++)scanf("%lf",&q[i]),b[i+n].r=q[i];39     for(i=0;i<=n<<1;i++)40     if(i<n)p[i]=-1.0/(1ll*(n-i)*(n-i));else41     if(i>n)p[i]=1.0/(1ll*(n-i)*(n-i));else p[i]=0;42     n<<=1;43     for(i=0;i<=n;i++)a[i].r=p[i];44     for(M=1;M<=n<<1;M<<=1)l++;45     for(i=0;i<M;i++)r[i]=(r[i>>1]>>1)|((i&1)<<l-1);46     FFT(a,M,1);FFT(b,M,1);47     for(i=0;i<M;i++)a[i]=a[i]*b[i];48     FFT(a,M,-1);49     for(i=n+1;i<=n+(n>>1);i++)printf("%.3lf\n",a[i].r);50     return 0;51 }
bzoj3527
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