luogu P3338 [ZJOI2014] force | FFT

I learned a room last fft chicken dish. .

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Push persimmon, sets of templates

Look for the bug, it fucks

#include<cmath>
#include<cstdio>
#include<complex>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long
const int N = 4e5+10;
const double pi=acos(-1.0);
typedef complex<double> E;
int n,m,L,rev[N];
E f[N],_f[N],g[N],e1[N],e2[N];
inline void fft(E *a,int op){
    for(int i=0;i<n;i++)
    if(rev[i]<i)swap(a[i],a[rev[i]]);
    for(int i=1;i<n;i<<=1){
        E wn(cos(pi/i),op*sin(pi/i));
        for(int j=0;j<n;j+=(i<<1)){
            E w(1,0);
            for(int k=0;k<i;k++,w*=wn){
                E x=a[j+k],y=w*a[j+k+i];
                a[j+k]=x+y; a[j+k+i]=x-y;
            }
        }
    }
    if(op==-1)for(int i=0;i<n;i++)a[i]/=n;
}
signed main(){
    cin>>n; n--;
    for(int i=0;i<=n;i++){
        double x; scanf("%lf",&x);
        f[i]=x; _f[n-i]=x;
    }
    for(int i=1;i<=n;i++)g[i]=(1.0/(i*i));
    m=2*n; for(n=1;n<=m;n<<=1)L++;
    for(int i=0;i<n;i++)rev[i]=(rev[i>>1]>>1)|((i&1)<<(L-1));
    fft(f,1); fft(g,1); fft(_f,1);
    for(int i=0;i<n;i++)e1[i]=f[i]*g[i];
    for(int i=0;i<n;i++)e2[i]=_f[i]*g[i];
    fft(e1,-1); fft(e2,-1);
    for(int i=0;i<=m/2;i++)
    printf("%.3lf\n",e1[i].real()-e2[m/2-i].real());
}