poj 2031Building a Space Station

http://poj.org/problem?id=2031

 1 #include<cstdio>

 2 #include<cstring>

 3 #include<cmath>

 4 #include<algorithm>

 5 const int inf=1<<23;

 6 #define maxn 110

 7 using namespace std;

 8 

 9 struct point

10 {

11     double x,y,z;

12     double r;

13 }p[110];

14 int n;

15 double g[maxn][maxn];

16 bool vis[maxn];

17 double dist[maxn],ans;

18 

19 double sqr(double a)

20 {

21     return a*a;

22 }

23 

24 inline double Sqrt(double a)

25 {

26     return a<=0?0:sqrt(a);

27 }

28 

29 double dis(point a,point b)

30 {

31     return (Sqrt(sqr(a.x-b.x)+sqr(a.y-b.y)+sqr(a.z-b.z))-a.r-b.r);

32 }

33 

34 bool prim()

35 {

36     memset(vis,false,sizeof(vis));

37     for(int i=0; i<n; i++)

38         dist[i]=inf;

39      ans=0;dist[1]=0;

40     for(int i=1; i<=n; i++)

41     {

42         double temp=inf;

43         int k=0;

44         for(int j=0; j<n; j++)

45         {

46             if(!vis[j]&&dist[j]<temp)

47             {

48                 temp=dist[j];

49                 k=j;

50             }

51         }

52         if(temp==inf) return false;

53         vis[k]=true;

54         ans+=temp;

55         for(int j=0; j<n; j++)

56         {

57             if(!vis[j]&&dist[j]>g[k][j])

58                 dist[j]=g[k][j];

59         }

60     }

61     return false;

62 }

63 

64 int main()

65 {

66     while(scanf("%d",&n)&&n){

67         memset(g,inf,sizeof(g));

68         for(int i=0; i<n; i++)

69         {

70             scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i].z,&p[i].r);

71         }

72         for(int i=0; i<n; i++)

73         {

74             for(int j=0; j<n; j++)

75             {

76                 if(dis(p[i],p[j])<=0)

77                 {

78                     g[i][j]=0;

79                 }

80                 else g[i][j]=dis(p[i],p[j]);

81             }

82         }

83         prim();

84         printf("%.3lf\n",ans);

85     }

86     return 0;

87 }

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