[AH2017/HNOI2017]礼物(FFT)

#include<iostream>
#include<cstdio>
#include<cmath>
#define N 200002
using namespace std;
typedef long long ll;
const double pai=acos(-1.0);
ll ans,sum,sum2,l,L,c[N];
int rev[N],n,m;
inline ll rd(){
    ll x=0;char c=getchar();bool f=0;
    while(!isdigit(c)){if(c==‘-‘)f=1;c=getchar();}
    while(isdigit(c)){x=(x<<1)+(x<<3)+(c^48);c=getchar();}
    return f?-x:x;
}
struct fs{
    double x,y;
    fs(){x=y=0;}
    fs(double xx,double yy){x=xx;y=yy;}
    fs operator +(const fs &b)const{return fs{x+b.x,y+b.y};}
    fs operator -(const fs &b)const{return fs{x-b.x,y-b.y};}
    fs operator *(const fs &b)const{return fs{x*b.x-y*b.y,x*b.y+y*b.x};}
}a[N],b[N];
inline void FFT(fs *a,int tag){
    for(int i=0;i<l;++i)if(i>rev[i])swap(a[i],a[rev[i]]);
    for(int i=1;i<l;i<<=1){
      fs wn(cos(pai/i),tag*sin(pai/i));
      for(int j=0;j<l;j+=(i<<1)){
          fs w(1,0); 
          for(int k=0;k<i;++k,w=w*wn){
              fs x=a[j+k],y=w*a[i+j+k];
              a[j+k]=x+y;a[i+j+k]=x-y;
        }
      } 
    }
}
int main(){
    n=rd();m=rd();
    for(int i=1;i<=n;++i)a[n-i+1].x=rd();
    for(int i=1;i<=n;++i){
      b[i].x=rd();
      sum+=a[i].x*a[i].x+b[i].x*b[i].x;
      sum2+=a[i].x-b[i].x;
    }
    l=1;L=0;
    while(l<(n<<1))l<<=1,L++;
    for(int i=1;i<l;++i)rev[i]=(rev[i>>1]>>1)|((i&1)<<(L-1));
    FFT(a,1);FFT(b,1);
    for(int i=0;i<l;++i)a[i]=a[i]*b[i];
    FFT(a,-1);
    for(int i=0;i<l;++i)a[i].x=(ll)(a[i].x/l+0.1);
    for(int i=1;i<=n;++i)a[i+n].x+=a[i].x;
    for(int i=n+1;i<=n<<1;++i){
        ans=max(ans,(ll)a[i].x);
    }
    ll x=1e18;
    for(int i=sum2/n-6;i<=sum2/n+6;++i)x=min(x,n*i*i+2*i*sum2);
    printf("%lld",sum-2*ans+x);
    return 0;
}