poj 1873

哇实验室里正在吵架，爽死了！

wf水题。显然二进制枚举，注意剪枝，val>ans的时候剪一下，不然会tle。然后就没惹。

我老人家一开始写了个

感觉非常垃圾，wa了一发又t了一发。

感觉自己可以退役了

#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
typedef double db;
#define pdd pair<db,db>
const db eps = 1e-6;
const db pi = acos(-1);
using namespace std;
int sign(db k){
    if (k>eps) return 1; else if (k<-eps) return -1; return 0;
}
int cmp(db k1,db k2){return sign(k1-k2);}
struct point{
    db x,y;
    db v,l;
    point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}
    point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
    point operator * (db k1) const{return (point){x*k1,y*k1};}
    point operator / (db k1) const{return (point){x/k1,y/k1};}
    bool operator <(const point &k1)const {
        int c=cmp(x,k1.x);
        if(c)return c==-1;
        return cmp(y,k1.y)==-1;
    }
    db abs(){ return sqrt(x*x+y*y);}
    db dis(point k1){return ((*this)-k1).abs();}
};
db cross(point k1,point k2){return k1.x*k2.y-k1.y*k2.x;}
db dot(point k1,point k2){return k1.x*k2.x+k1.y*k2.y;}
vector<point> convexHull(vector<point> ps){
    int n = ps.size();if(n<=1)return ps;
    sort(ps.begin(),ps.end());
    vector<point> qs(n*2);int k=0;
    for(int i=0;i<n;qs[k++]=ps[i++])
        while (k>1&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-2])<=0)--k;
    for(int i=n-2,t=k;i>=0;qs[k++]=ps[i--])
        while (k>t&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-2])<=0)--k;
    qs.resize(k-1);
    return qs;
}
int n;
point p[19];
vector<point> v;
db res=0,sum=1e9;int ans=-1;
void slove(int x){
    v.clear();
    db l1=0,val=0;
    for(int i=0;i<n;i++){
        if(1&(x>>i)){//砍了
            l1+=p[i].l;
            val+=p[i].v;
        } else{
            v.push_back(p[i]);
        }
    }
    if(cmp(val,sum)>=0)
        return;
    v=convexHull(v);
    db l2=0;
    for(int i=0;i<v.size();i++){
        l2+=v[i].dis(v[(i+1)%v.size()]);
    }
    if(v.size()==1)l2=0;
    if(cmp(l1,l2)>=0){//阔以
        sum=val;
        res=l1-l2;
        ans=x;
    }
}
int main(){
    int cas = 0;
    while (scanf("%d",&n)&&n){
        cas++;
        for(int i=0;i<n;i++){
            scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i].v,&p[i].l);
        }
        for(int i=1;i<(1<<n)-1;i++){
            slove(i);
        }
        if(cas>=2)printf("
");
        printf("Forest %d
",cas);
        printf("Cut these trees:");
        for(int i=0;i<n;i++){
            if((ans>>i)&1){
                printf(" %d",i+1);
            }
        }
        printf("
Extra wood: %.2f
",res);
        res=0,sum=1e9;
    }
}