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 ",++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 ",o[num-1]); 137 printf("Extra wood: %.2f ",res); 138 } 139 return 0; 140 }