poj 1873The Fortified Forest (凸包二进制枚举)

注意：

一共n位，所以i从1枚举到 (1<

#include <iostream>
#include <cmath>
#include <cstdio>
#include <string.h>
#include <algorithm>
#define pi acos(-1)
#define eps 1e-8
using namespace std;struct point{double x,y,v,len;int num;point(){}point(double xx,double yy){x=xx,y=yy;}double operator * (point t){return x*t.y - t.x*y;}point operator - (point t){return point(x-t.x,y-t.y);}
}a[20],b[20];
bool cmp(point a,point b){return a.x < b.x;
}
double dis(point a,point b){return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) );
}
point stak[1000];
int vis[200],needv;double sumlen = 0,needlen = 0;double graham(int n){for(int i = 1;i <= n;i++){b[i] = a[i];}sort(b+1, b+1+n,cmp);int r,top=0,m;for(int i = 1; i <= n; i++) {if(vis[ b[i].num ] == 1) continue;while(top>1 && (stak[top]-stak[top-1])*(b[i]-stak[top]) <= 0 ) top--;stak[++top] = b[i];}m = top;for(int i = n-1; i >= 1; i--) {if(vis[b[i].num] == 1) continue;while(top>m && (stak[top]-stak[top-1])*(b[i]-stak[top]) <= 0 ) top--;stak[++top] = b[i];}for(int i = 2;i<=top;i++){needlen += dis(stak[i],stak[i-1]);}return needlen;
}
int  f(int i){memset(vis,0,sizeof(vis));sumlen = 0,needlen = 0,needv=0;int cnt = 0;for(int j = 1;i != 0;i>>=1,j++){if(i&1){vis[j] = 1;sumlen += a[j].len;cnt++;needv += a[j].v;}}return cnt;
}int main(){int n,l,ncase=0;while(~scanf("%d",&n),n){ncase++;for(int i = 1;i <= n;i++){scanf("%lf%lf%lf%lf",&a[i].x,&a[i].y,&a[i].v,&a[i].len);a[i].num = i;}int delimiter = (1<<(n));int ans = 100;int ansi = 0,ansv = 0x3f3f3f3f;for(int i = 1;i < delimiter;i++){int cnt_del = f(i);if(needv > ansv) continue;graham(n);if(needlen <= sumlen+eps && ansv > needv){ans = cnt_del,ansi = i;ansv = needv;}else if(needlen <= sumlen+eps && ansv == needv && ans > cnt_del){ansi = i;ans = cnt_del;}}f(ansi);graham(n);printf("Forest %d\n",ncase);printf("Cut these trees: ");for(int i = 1;i <= n;i++){if(vis[i] == 1)printf("%d ",i);}puts("");printf("Extra wood: %.2f\n\n",sumlen-needlen);}return 0;
}

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