bzoj4827: [Hnoi2017]礼物

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long LL;
LL sqr(LL x){return x*x;}

const double pi=acos(-1.0);
struct complex
{
	double r,i;
	complex(){}
	complex(double R,double I){r=R,i=I;}
	friend complex operator +(complex x,complex y){return complex(x.r+y.r,x.i+y.i);}
	friend complex operator -(complex x,complex y){return complex(x.r-y.r,x.i-y.i);}
	friend complex operator *(complex x,complex y){return complex(x.r*y.r-x.i*y.i,x.r*y.i+x.i*y.r);}
}A[410000],B[410000],C[410000]; int Re[410000];
void fft(complex *a,int n,int op)
{
    for(int i=0;i<n;i++)
        if(i<Re[i])swap(a[i],a[Re[i]]);
        
    for(int i=1;i<n;i<<=1)
    {
        complex wn(cos(pi/i),sin(op*pi/i));
        for(int j=0;j<n;j+=(i<<1))
        {
            complex w(1,0);
            for(int k=0;k<i;k++,w=w*wn)
            {
                complex t1=a[j+k],t2=a[j+k+i]*w;
                a[j+k]=t1+t2;a[j+k+i]=t1-t2;
            }
        }
    }
}

int len,n,aa[51000],bb[51000];
LL solve(int CC)
{
	memset(A,0,sizeof(A));
	memset(B,0,sizeof(B));
	LL sum=0;
	for(int i=0;i<len;i++)
	{
		A[i].r=A[len+i].r=aa[i]+CC, B[i].r=bb[len-1-i];
		sum+=sqr(aa[i]+CC)+sqr(bb[len-1-i]);
	}
	
	fft(A,n,1),fft(B,n,1);
	for(int i=0;i<n;i++)C[i]=A[i]*B[i];
	fft(C,n,-1);
	
	LL ret=(1LL<<62);
	for(int i=len-1;i<=2*(len-1);i++)
		ret=min(ret,sum-2*LL(C[i].r/n+0.5));
	return ret;
}
int main()
{
	freopen("a.in","r",stdin);
	freopen("a.out","w",stdout);
	int M; LL sum=0;
	scanf("%d%d",&len,&M);
	for(int i=0;i<len;i++)scanf("%d",&aa[i]),sum+=aa[i];
	for(int i=0;i<len;i++)scanf("%d",&bb[i]),sum-=bb[i];
	sum/=len;
	
	int m=len*3,L=0;
	for(n=1;n<=m;n*=2)L++;
	for(int i=1;i<=n;i++)Re[i]=(Re[i>>1]>>1)|((i&1)<<(L-1));
	
	LL mmin=(1LL<<62);
	for(int C=sum-1;C<=sum+1;C++)
		mmin=min(mmin,solve(C));
	printf("%lld\n",mmin);
	
	return 0;
}