POJ 2560

#include<iostream>
#include<algorithm>
#include<cmath>
#include<iomanip>
#define MAXN 105
#define inf 1000000000
using namespace std;

typedef double elem_t;

double point[MAXN][2];
double _m[MAXN][MAXN];
int pre[MAXN];
elem_t prim(int n,elem_t mat[][MAXN],int* pre);
int main()
{
    //freopen("acm.acm","r",stdin);
    int num;
    int i;
    int j;
    double x;
    double y;
    cin>>num;
    for(i = 0; i < num; ++ i)
    {
        cin>>point[i][0]>>point[i][1];    
    }
    for(i = 0; i < num; ++ i)
    {
        for(j = i+1; j < num; ++ j)
        {
            _m[i][j] = sqrt((point[i][0] - point[j][0])*(point[i][0] - point[j][0]) + (point[i][1] - point[j][1])*(point[i][1] - point[j][1]));
            _m[j][i] = _m[i][j];
        }
    }
    cout<<setiosflags(ios::fixed)<<setprecision(2)<<prim(num,_m,pre)<<endl;
}


elem_t prim(int n,elem_t mat[][MAXN],int* pre){
    elem_t min[MAXN],ret=0;
    int v[MAXN],i,j,k;
    for (i=0;i<n;i++)
        min[i]=inf,v[i]=0,pre[i]=-1;
    for (min[j=0]=0;j<n;j++){
        for (k=-1,i=0;i<n;i++)
            if (!v[i]&&(k==-1||min[i]<min[k]))
                k=i;
        for (v[k]=1,ret+=min[k],i=0;i<n;i++)
            if (!v[i]&&mat[k][i]<min[i])
                min[i]=mat[pre[i]=k][i];
    }
    return ret;
}