bzoj1091

题解：

暴力枚举顺序

然后计算几何

代码：

#include<bits/stdc++.h>
int n,id[11],lp=0;
double v1,v2,ans=1e10;
struct pos
{
    double x,y;
    void init(){scanf("%lf%lf",&x,&y);}
    pos operator+(pos a){return (pos){x+a.x,y+a.y};}
    pos operator-(pos a){return (pos){x-a.x,y-a.y};}
    pos operator*(double a){return (pos){x*a,y*a};}
    double operator*(pos a){return x*a.y-y*a.x;}
    double dot(pos a){return x*a.x+y*a.y;}
    double abs(){return sqrt(x*x+y*y);}
}ps[11];
double mn,mx;
struct line
{
    pos a,b;
    void chk(line w)
     {
        double c=w.b*b;
        if(c==0)return;
        c=(a*w.b+w.b*w.a)/c;
        if(c>0.5)c<mx&&(mx=c);
        else c>mn&&(mn=c);
     }
}ls[15],l0[11];
int main()
{
    scanf("%lf%lf%d",&v1,&v2,&n);
    for (int i=1;i<=n;i++)ps[i].init(),id[i]=i;
    ps[n+1]=ps[1];
    pos p1=(pos){0,0},p2=(pos){v1,0},p3=(pos){v1,v2},p4=(pos){0,v2};
    ls[lp++]=(line){p1,p2-p1};
    ls[lp++]=(line){p2,p3-p2};
    ls[lp++]=(line){p3,p4-p3};
    ls[lp++]=(line){p4,p1-p4};
    for (int i=1;i<=n;++i)l0[i]=(line){ps[i],ps[i+1]-ps[i]};
    do
     {
        lp=4;
        double s=0;
        for (int i=1;i<=n;i++)
         {
            int w=id[i];
            mn=-1e10,mx=1e10;
            for (int j=0;j<lp;j++)l0[w].chk(ls[j]);
            ls[lp++]=l0[w];
            s+=(mx-mn)*l0[w].b.abs();
         }
        if (s<ans)ans=s;
     }while(std::next_permutation(id+1,id+n+1));
    printf("%.3f",ans);
    return 0;
}