bzoj2428: [HAOI2006]均分数据

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;
double sqr(double x){return x*x;}
double drand(){return double(rand()%10000)/10000.0;}

int n,m,p[30];double a[30],mmin;
double sum[30];
double calc()
{
    memset(sum,0,sizeof(sum));
    for(int i=1;i<=n;i++)sum[p[i]]+=a[i];
    
    double ave=0;
    for(int i=1;i<=m;i++)ave+=sum[i];
    ave/=double(m);
        
    double ret=0;
    for(int i=1;i<=m;i++)ret+=sqr(ave-sum[i]);
    ret=sqrt(ret/(double)m);
    if(ret<mmin)mmin=ret;
    return ret;
}
void annealing()
{
    double T=1000000.0;

    while(T>1)
    {
        double k1=calc();
        
        int pp=1;
        for(int i=1;i<=m;i++)
            if(sum[i]<sum[pp])pp=i;
            
        int x=rand()%n+1,np;
        while(p[x]==pp){x++;if(x==n+1)x=1;}
        
        np=p[x],p[x]=pp;
        double k2=calc();
        
        if(k1>k2||exp((k1-k2)/T)>drand());
        else p[x]=np;
        
        T*=0.9997;
    }
    
    while(T>0.0001)
    {
        int x=rand()%n+1,pp=rand()%m+1,np;
        if(pp==p[x]){pp++;if(pp==m+1)pp=1;}
        
        double k1=calc();
        np=p[x],p[x]=pp;
        double k2=calc();
        
        if(k1>k2||exp((k1-k2)/T)>drand());
        else p[x]=np;
        
        T*=0.9997;
    }
    
    for(int i=1;i<=1000;i++)
    {
        int x=rand()%n+1,pp=rand()%m+1,np;
        if(pp==p[x]){pp++;if(pp==m+1)pp=1;}
        
        double k1=calc();
        np=p[x],p[x]=pp;
        double k2=calc();
        p[x]=np;
    }
}

int main()
{
    srand(25424);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)
        scanf("%lf",&a[i]), p[i]=rand()%m+1;
    random_shuffle(a+1,a+n+1);
    
    mmin=calc();
    annealing();
    printf("%.2lf",mmin);
    return 0;
}