首页 > 代码库 > POJ 1873

POJ 1873

按位枚举,按最小价值,最小砍掉树剪枝就好了。

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;const int MAXN=20;const int inf=190000000;int n,l;int st[MAXN],stop,cnt;int ans[MAXN];bool cut[MAXN];struct point{	int x,y;	int len,val;	int num;}p[MAXN];int ansV,ansC;double anslen;bool cmp(point A,point B){	if(A.y<B.y) return true;	else if(A.y==B.y){		if(A.x<B.x) return true;	}	return false;}bool cmp1(int a,int b){	if(a<b) return true;	return false;}bool multi(point a,point b,point c){	return (a.x-c.x)*(b.y-c.y)-(a.y-c.y)*(b.x-c.x)<=0;}double dist(point a, point b){	return sqrt((a.x-b.x)*(a.x-b.x)*1.0+(a.y-b.y)*(a.y-b.y)*1.0);}double for_len(){	if(cnt==1) return 0;	double res=0;	for(int i=1;i<cnt;i++)	res+=dist(p[ans[i]],p[ans[i-1]]);	return (res);}void slove(){	stop=0; cnt=0;	int choice=0; int be;	for(int i=0;i<n;i++){		if(!cut[i]){			st[stop++]=i;			choice++;		}		if(choice==2){ 			be=i;			break;		}	}	if(choice<2){ cnt=1; return ; }	for(int i=be+1;i<n;i++){		if(cut[i]) continue;		while(stop>1&&multi(p[st[stop-1]],p[i],p[st[stop-2]])) stop--;		st[stop++]=i;	}	for(int i=0;i<stop;i++){		ans[cnt++]=st[i];	}	stop=0; choice=0;	for(int i=n-1;i>=0;i--){		if(!cut[i]){			st[stop++]=i;			choice++;		}		if(choice==2){ be=i; break; }	}	for(int i=be-1;i>=0;i--){		if(cut[i]) continue;		while(stop>1&&multi(p[st[stop-1]],p[i],p[st[stop-2]])) stop--;		st[stop++]=i;	}	for(int i=0;i<stop;i++)	ans[cnt++]=st[i];}int main(){	int cas=0;	while(scanf("%d",&n)!=EOF){		if(n==0) break;		cas++;		for(int i=0;i<n;i++){			scanf("%d%d%d%d",&p[i].x,&p[i].y,&p[i].val,&p[i].len);			p[i].num=i+1;		}		sort(p,p+n,cmp);		ansV=inf; int tmpV; int tmpC; double len; int CUT=inf;		for(int i=1;i<(1<<n);i++){			tmpV=0; tmpC=0; len=0;			memset(cut,false,sizeof(cut));			for(int k=0;k<n;k++){				if((1<<k)&i){					cut[k]=true;					tmpV+=p[k].val;					tmpC++;					len+=p[k].len;				}			}			if(tmpV<ansV){				slove();				double res=for_len();				if(res<=len){					CUT=tmpC;					ansV=tmpV;					ansC=i;					anslen=len*1.0-res;				}			}			else if(tmpV==ansV){				if(CUT>tmpC){					slove();					double res=for_len();					if(res<=len){						CUT=tmpC;						ansV=tmpV;						ansC=i;						anslen=len*1.0-res;					}				}			}		}		printf("Forest %d\n",cas);		printf("Cut these trees:");		cnt=0;		for(int k=0;k<n;k++)		if((1<<k)&ansC){			st[cnt++]=p[k].num;		}		sort(st,st+cnt,cmp1);		for(int i=0;i<cnt;i++)		printf(" %d",st[i]);		printf("\n");		printf("Extra wood: %0.2lf\n",anslen);		printf("\n");	}	return 0;}