poj1873The Fortified Forest

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居然是WF的水题~

二进制枚举砍哪些树，剩余的树围成一个凸包。

因为传数组WA了两发，忘记修改排序数组中的p[0];

  1 #include <iostream>

  2 #include<cstdio>

  3 #include<cstring>

  4 #include<algorithm>

  5 #include<stdlib.h>

  6 #include<vector>

  7 #include<cmath>

  8 #include<queue>

  9 #include<set>

 10 using namespace std;

 11 #define N 20

 12 #define LL long long

 13 #define INF 0xfffffff

 14 const double eps = 1e-8;

 15 const double pi = acos(-1.0);

 16 const double inf = ~0u>>2;

 17 struct point

 18 {

 19     int x,y;

 20     int vi,li;

 21     point(int x=0,int y=0):x(x),y(y){}

 22 }p[N],q[N],ch[N];

 23 int o[N],f[N];

 24 typedef point pointt;

 25 pointt operator -(point a,point b)

 26 {

 27     return point(a.x-b.x,a.y-b.y);

 28 }

 29 int dcmp(double x)

 30 {

 31     if(fabs(x)<eps) return 0;

 32     return x<0?-1:1;

 33 }

 34 double cross(point a,point b)

 35 {

 36     return 1.0*a.x*b.y-a.y*b.x;

 37 }

 38 double mul(point p0,point p1,point p2)

 39 {

 40     return cross(p1-p0,p2-p0);

 41 }

 42 double dis(point a)

 43 {

 44     return sqrt(1.0*a.x*a.x+a.y*a.y);

 45 }

 46 bool cmp(point a,point b)

 47 {

 48     if(dcmp(mul(q[0],a,b))==0)

 49         return dis(a-q[0])<dis(b-q[0]);

 50     else

 51         return dcmp(mul(q[0],a,b))>0;

 52 }

 53 double Graham(int n)

 54 {

 55     if(n<=1) return 0;

 56     if(n==2) return 2*dis(q[0]-q[1]);

 57     int i,k = 0,top;

 58     point tmp;

 59     for(i = 0 ; i < n; i++)

 60     {

 61         if(q[i].y<q[k].y||(q[i].y==q[k].y&&q[i].x<q[k].x))

 62             k = i;

 63     }

 64     if(k!=0)

 65     {

 66         tmp = q[0];

 67         q[0] = q[k];

 68         q[k] = tmp;

 69     }

 70     sort(q+1,q+n,cmp);

 71     ch[0] = q[0];

 72     ch[1] = q[1];

 73     top = 1;

 74     for(i = 2; i < n ; i++)

 75     {

 76         while(top>0&&dcmp(mul(ch[top-1],ch[top],q[i]))<0)

 77             top--;

 78         top++;

 79         ch[top] =q[i];

 80     }

 81     ch[top+1] = ch[0];

 82     double len = 0;

 83     for(i = 0 ; i <= top ; i++)

 84     len+=dis(ch[i]-ch[i+1]);

 85     return len;

 86 }

 87 int main()

 88 {

 89     int n,i,j,g;

 90     int kk = 0;

 91     while(scanf("%d",&n)&&n)

 92     {

 93         for(i = 0 ; i <n ;i++)

 94         scanf("%d%d%d%d",&p[i].x,&p[i].y,&p[i].vi,&p[i].li);

 95         int num;

 96         int ans = INF;

 97         double res = 0;

 98         for(i = 0 ; i < (1<<n) ; i++)

 99         {

100             g = 0;

101             int gg = 0;

102             int tv = 0;

103             double tlen = 0;

104             for(j = 0 ;j < n; j++)

105             {

106                 if((1<<j)&i)

107                 {

108                     f[gg++] = j;

109                     tlen+=p[j].li;

110                     tv += p[j].vi;

111                 }

112                 else q[g++] = p[j];

113             }

114             double len = Graham(g);

115             if(dcmp(tlen-len)>=0)

116             {

117                 if(ans>tv||(ans==tv&&num>gg))

118                 {

119                     ans = tv;

120                     num = gg;

121                     res = tlen-len;

122                     //cout<<len<<" "<<i<<endl;

123                     

124                     

125                     for(j = 0 ; j < gg ; j++)

126                     o[j] = f[j]+1;

127                 }

128             }

129         }

130         if(kk) puts("");

131         printf("Forest %d\n",++kk);

132         printf("Cut these trees: ");

133         for(i = 0; i < num-1; i++)

134         printf("%d ",o[i]);

135         if(num)

136         printf("%d\n",o[num-1]);

137         printf("Extra wood: %.2f\n",res);

138     }

139     return 0;

140 }

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