POJ 2253

 #include<iostream>
 #include<stdio.h>
 #include<math.h>
 #include<iomanip>
 #define MAXN 250
 #define inf 1000000000
 typedef double elem_t;

 using namespace std;

 double _m[MAXN][MAXN];
 struct point
 {
     double a;
     double b;
 };
 elem_t prim(int n,elem_t mat[][MAXN],int* pre);
 point p[];
 int pre[];
 int main()
 {
     //freopen("acm.acm","r",stdin);
     int num;
     int max = ;
     int i;
     int time = ;
     int j;
     int value;
     while(cin>>num)
     {
         if(!num)
             break;
         cin>>p[].a;
         cin>>p[].b;
         cin>>p[].a;
         cin>>p[].b;
         memset(_m,,sizeof(_m));
         for(i = ; i < num; ++ i)
         {
             cin>>p[i].a;
             cin>>p[i].b;
         }
         for(i = ; i < num; ++ i)
         {
             for(j = i; j < num; ++ j)
             {
                 _m[i][j] = (p[i].a - p[j].a)*(p[i].a - p[j].a) + (p[i].b - p[j].b)*(p[i].b - p[j].b);
                 _m[j][i] = _m[i][j];
             }
         }
         prim(num,_m,pre);
         i = ;
         while()
         {
             if(_m[i][pre[i]] > max)
             {
                 max = _m[i][pre[i]];
             }
             if(pre[i] == )
                 break;
             i = pre[i];
         }
         cout<<"Scenario #"<<++ time<<endl
             <<"Frog Distance = "
             <<setiosflags(ios::fixed)<<setprecision()<<sqrt(long double (max))<<endl
             <<endl;
         max = ;
     }

 }

 elem_t prim(int n,elem_t mat[][MAXN],int* pre){
     elem_t min[MAXN],ret=;
     int v[MAXN],i,j,k;
     for (i=;i<n;i++)
         min[i]=inf,v[i]=,pre[i]=-;
     for (min[j=]=;j<n;j++){
         for (k=-,i=;i<n;i++)
             if (!v[i]&&(k==-||min[i]<min[k]))
                 k=i;
         for (v[k]=,ret+=min[k],i=;i<n;i++)
             if (!v[i]&&mat[k][i]<min[i])
                 min[i]=mat[pre[i]=k][i];
     }
     return ret;
 }

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