The Fortified Forest POJ

The Fortified Forest

 POJ - 1873

题意：n棵树，砍掉一些树做木材将剩余的树围起来。

n较小，二进制枚举~

#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
const double eps=1e-12;
const int inf=0x3f3f3f3f;
const int maxn=16;
struct Node{
    int x,y,vi,li;
    bool operator < (const Node& a)const{
        return x<a.x||x==a.x&&y<a.y;
    }
    Node operator - (const Node& a){
        return Node{x-a.x,y-a.y};
    }
}p[maxn],vex[maxn],ch[maxn];
double getdis(Node a,Node b){
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int cut[maxn],ans[maxn];

int cross(Node a,Node b){
    return a.x*b.y-a.y*b.x;
}

double ConvexHull(Node *p,int n){
    if(n<=1) return 0;
    sort(p,p+n);
    int m=0;
    for(int i=0;i<n;i++){
        while(m>1&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
        ch[m++]=p[i];
    }
    int k=m;
    for(int i=n-2;i>=0;i--){
        while(m>k&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
        ch[m++]=p[i];
    }
    m--;
    double ans=getdis(ch[0],ch[m]);
    for(int i=0;i<m;i++) ans+=getdis(ch[i],ch[i+1]);
    return ans;
}
int main(){
    int n,kase=0;
    while(scanf("%d",&n)&&n){
        if(kase) puts("");
        for(int i=0;i<n;i++) scanf("%d%d%d%d",&p[i].x,&p[i].y,&p[i].vi,&p[i].li);
        int sta=1<<n;
        int minval=inf,id;
        double res;
        int tempval,templen;
        for(int i=1;i<sta;i++){
            int cnt=0,num=0;
            tempval=0;templen=0;
            for(int j=0;j<n;j++) if((1<<j)&i){
                cut[cnt++]=j;
                tempval+=p[j].vi;
                templen+=p[j].li;
            }else {
                vex[num++]=p[j];
            }
            double dis=ConvexHull(vex,num);
            if(templen>dis&&(tempval<minval||tempval==minval&&cnt<id)){
                minval=tempval;
                res=templen-dis;
                id=cnt;
                for(int i=0;i<cnt;i++) ans[i]=cut[i];
            }
        }
        printf("Forest %d
",++kase);
        printf("Cut these trees:");
        for(int i=0;i<id;i++) printf(" %d",ans[i]+1);
        printf("
Extra wood: %.2f
",res);
    }
    return 0;
}