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

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cmath>
 4 #include <iostream>
 5 #include <iomanip>
 6 #include <algorithm>
 7 #include <vector>
 8 typedef double db;
 9 #define pdd pair<db,db>
10 const db eps = 1e-6;
11 const db pi = acos(-1);
12 using namespace std;
13 int sign(db k){
14     if (k>eps) return 1; else if (k<-eps) return -1; return 0;
15 }
16 int cmp(db k1,db k2){return sign(k1-k2);}
17 struct point{
18     db x,y;
19     db v,l;
20     point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}
21     point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
22     point operator * (db k1) const{return (point){x*k1,y*k1};}
23     point operator / (db k1) const{return (point){x/k1,y/k1};}
24     bool operator <(const point &k1)const {
25         int c=cmp(x,k1.x);
26         if(c)return c==-1;
27         return cmp(y,k1.y)==-1;
28     }
29     db abs(){ return sqrt(x*x+y*y);}
30     db dis(point k1){return ((*this)-k1).abs();}
31 };
32 db cross(point k1,point k2){return k1.x*k2.y-k1.y*k2.x;}
33 db dot(point k1,point k2){return k1.x*k2.x+k1.y*k2.y;}
34 vector<point> convexHull(vector<point> ps){
35     int n = ps.size();if(n<=1)return ps;
36     sort(ps.begin(),ps.end());
37     vector<point> qs(n*2);int k=0;
38     for(int i=0;i<n;qs[k++]=ps[i++])
39         while (k>1&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-2])<=0)--k;
40     for(int i=n-2,t=k;i>=0;qs[k++]=ps[i--])
41         while (k>t&&cross(qs[k-1]-qs[k-2],ps[i]-qs[k-2])<=0)--k;
42     qs.resize(k-1);
43     return qs;
44 }
45 int n;
46 point p[19];
47 vector<point> v;
48 db res=0,sum=1e9;int ans=-1;
49 void slove(int x){
50     v.clear();
51     db l1=0,val=0;
52     for(int i=0;i<n;i++){
53         if(1&(x>>i)){//砍了
54             l1+=p[i].l;
55             val+=p[i].v;
56         } else{
57             v.push_back(p[i]);
58         }
59     }
60     if(cmp(val,sum)>=0)
61         return;
62     v=convexHull(v);
63     db l2=0;
64     for(int i=0;i<v.size();i++){
65         l2+=v[i].dis(v[(i+1)%v.size()]);
66     }
67     if(v.size()==1)l2=0;
68     if(cmp(l1,l2)>=0){//阔以
69         sum=val;
70         res=l1-l2;
71         ans=x;
72     }
73 }
74 int main(){
75     int cas = 0;
76     while (scanf("%d",&n)&&n){
77         cas++;
78         for(int i=0;i<n;i++){
79             scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i].v,&p[i].l);
80         }
81         for(int i=1;i<(1<<n)-1;i++){
82             slove(i);
83         }
84         if(cas>=2)printf("\n");
85         printf("Forest %d\n",cas);
86         printf("Cut these trees:");
87         for(int i=0;i<n;i++){
88             if((ans>>i)&1){
89                 printf(" %d",i+1);
90             }
91         }
92         printf("\nExtra wood: %.2f\n",res);
93         res=0,sum=1e9;
94     }
95 }