POJ-2031 Building a Space Station 最小生成树

　　题目链接：http://poj.org/problem?id=2031

　　很典型的最小生成树题目。

 1 //STATUS:C++_AC_0MS_252KB

 2 #include<stdio.h>

 3 #include<stdlib.h>

 4 #include<string.h>

 5 #include<math.h>

 6 #include<iostream>

 7 #include<string>

 8 #include<algorithm>

 9 #include<vector>

10 #include<queue>

11 #include<stack>

12 using namespace std;

13 #define LL __int64

14 #define pii pair<int,int>

15 #define Max(a,b) ((a)>(b)?(a):(b))

16 #define Min(a,b) ((a)<(b)?(a):(b))

17 #define mem(a,b) memset(a,b,sizeof(a))

18 #define lson l,mid,rt<<1

19 #define rson mid+1,r,rt<<1|1

20 const int N=110,M=1000000,INF=0x3f3f3f3f,MOD=1999997;

21 const LL LLNF=0x3f3f3f3f3f3f3f3fLL;

22 const double DNF=100000000;

23 

24 struct Node{

25     double x,y,z,r;

26 }nod[N];

27 double w[N][N],d[N];

28 int vis[N];

29 int n;

30 

31 inline double dist(Node &a,Node &b)

32 {

33     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)

34                 +(a.z-b.z)*(a.z-b.z));

35 }

36 

37 double mintree()

38 {

39     int i,j,x;

40     double m,ans=0;

41     for(i=0;i<n;i++)d[i]=DNF;

42     d[0]=0;

43     mem(vis,0);

44     for(i=0;i<n;i++){

45         m=DNF;

46         for(j=0;j<n;j++)if(d[j]<m && !vis[j])m=d[x=j];

47         vis[x]=1;

48         ans+=d[x];

49         for(j=0;j<n;j++){

50             if(w[x][j]<d[j] && !vis[j])

51                 d[j]=w[x][j];

52         }

53     }

54     return ans;

55 }

56 

57 int main()

58 {

59  //   freopen("in.txt","r",stdin);

60     int i,j;

61     double t;

62     while(~scanf("%d",&n) && n)

63     {

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

65             for(j=0;j<n;j++)w[i][j]=DNF;

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

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

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

69             for(j=i;j<n;j++){

70                 t=dist(nod[i],nod[j])-nod[i].r-nod[j].r;

71                 w[i][j]=w[j][i]=t>0?t:0;

72             }

73         }

74 

75         printf("%.3lf\n",mintree());

76     }

77     return 0;

78 }