bzoj2515 Room

Description

Input

Output

折半搜索，用散列表记录从原点出发，用了S（状压表示）这几种边（令|S|*2-1<=n），到达(x,y)的最大面积。

#include<cstdio>
#include<cmath>
#include<algorithm>
int ps[][][],pp[],r[],n,ed[],st=,ans;
#define cal(w,x,y,a,b,s) dfs(w,x+(a),y+(b),s+x*(b)-y*(a))
const int P=;
int h[P][],ht=,ds[];
void maxs(int&a,int b){if(a<b)a=b;}
void mins(int&a,int b){if(a>b)a=b;}
void ins(int st,int x,int y,int s){
    int X,w,st2=(<<n)--st;
    if(ds[st2]==ht){
        X=(x+<<|y+)<<|st2;
        w=X%P;
        while(h[w][]==ht){
            if(h[w][]==X){
                maxs(ans,h[w][]+s);
                break;
            }
            if((w+=)>=P)w-=P;
        }
    }else{
        ds[st]=ht;
        X=(x+<<|y+)<<|st;
        w=X%P;
        while(h[w][]==ht){
            if(h[w][]==X){
                maxs(h[w][],s);
                return;
            }
            if((w+=)>=P)w-=P;
        }
        h[w][]=ht;
        h[w][]=X;
        h[w][]=s;
    }
}
void dfs(int w,int x,int y,int s){
    if(w)ins(st,x,y,s);
    if(w<)
    for(int i=;i<n;++i)if(!ed[i]){
        ed[i]=;
        st^=<<i;
        int v=r[i];
        for(int j=;j<pp[v];++j){
            int a=ps[v][j][],b=ps[v][j][];
            cal(w+,x,y,a,b,s);
            cal(w+,x,y,a,-b,s);
            cal(w+,x,y,-a,b,s);
            cal(w+,x,y,-a,-b,s);
            cal(w+,x,y,b,a,s);
            cal(w+,x,y,b,-a,s);
            cal(w+,x,y,-b,a,s);
            cal(w+,x,y,-b,-a,s);
        }
        st^=<<i;
        ed[i]=;
    }
}
int main(){
    for(int i=;i<=;++i){
        for(int j=;j*j*<=i*i;++j){
            int z=sqrt(i*i-j*j)+1e-;
            if(j*j+z*z==i*i)ps[i][pp[i]][]=j,ps[i][pp[i]++][]=z;
        }
    }
    while(scanf("%d",&n)==&&n){
        for(int i=;i<n;++i)scanf("%d",r+i);
        ans=;
        ++ht;
        dfs(,,,);
        if(!ans)puts("-1");
        else if(~ans&)printf("%d\n",ans>>);
        else printf("%d.5\n",ans>>);
    }
    return ;
}