poj1873（二进制枚举+求凸包周长）

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;

const int maxn=20;
const int inf=0x3f3f3f3f;

struct Point{
    int x,y;
    Point():x(0),y(0){}
    Point(int x,int y):x(x),y(y){}
};

int n,cas,val,num,res[maxn],v[maxn],l[maxn],vis[maxn];
double ext;
int top,stack[maxn];
Point pt[maxn],list[maxn];

int cross(Point p0,Point p1,Point p2){
    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}

double dis(Point p1,Point p2){
    return sqrt((double)(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y));
}

bool cmp(Point p1,Point p2){
    int tmp=cross(list[0],p1,p2);
    if(tmp>0) return true;
    else if(tmp==0&&dis(list[0],p1)<dis(list[0],p2)) return true;
    else return false;
}

void init(int m){
    Point p0=list[0];
    int k=0;    
    for(int i=1;i<m;++i){
        if((p0.y>list[i].y)||((p0.y==list[i].y)&&(p0.x>list[i].x))){
            p0=list[i];
            k=i;
        }
    }
    list[k]=list[0];
    list[0]=p0;
    sort(list+1,list+m,cmp);
}

double graham(int m){
    if(m==1){
        top=0;
        stack[0]=0;
    }
    else{
        top=1;
        stack[0]=0;
        stack[1]=1;
        for(int i=2;i<m;++i){
            while(top>0&&cross(list[stack[top-1]],list[stack[top]],list[i])<=0) --top;
            stack[++top]=i;
        }
    }
    double ret=0;
    for(int i=0;i<top;++i)
        ret+=dis(list[stack[i]],list[stack[i+1]]);
    ret+=dis(list[stack[top]],list[stack[0]]);
    return ret;
}

int main(){
    while(scanf("%d",&n),n){
        val=num=inf;
        for(int i=0;i<n;++i)
            scanf("%d%d%d%d",&pt[i].x,&pt[i].y,&v[i],&l[i]);
        for(int i=1;i<(1<<n)-1;++i){
            int t1=0,t2=0,cnt=0;
            for(int j=0;j<n;++j){
                if((i>>j)&1){
                    t1+=v[j],t2+=l[j];
                }
                else{
                    list[cnt++]=pt[j];
                }
            }
            init(cnt);
            int cnt2=n-cnt;
            if((t1<val)||((t1==val)&&(cnt2<num))){
                double tmp=graham(cnt);
                if(tmp>t2) continue;
                val=t1,num=cnt2,ext=t2-tmp;
                int t=0;
                for(int j=0;j<n;++j){
                    if((i>>j)&1)
                        res[t++]=j;
                }
            }
        }
        printf("Forest %d\nCut these trees:",++cas);
        for(int i=0;i<num;++i)
            printf(" %d",res[i]+1);
        printf("\nExtra wood: %.2f\n\n",ext);
    }
    return 0;
}