（最小生成树）Eddy's picture -- hdu -- 1162

#include <iostream>
#include <cstdio>
#include <cstring>
#include <stdlib.h>
#include <math.h>
#include <queue>
#include <algorithm>
using namespace std;

const int oo = 0x3f3f3f3f;
const int N = 110;

struct node
{
    double x, y;
}s[N];

int n, vis[N];
double dist[N], G[N][N];

double prim()
{
    double ans = 0;
    for(int i=1; i<=n; i++)
        dist[i] = G[1][i];

    memset(vis, 0, sizeof(vis));
    vis[1] = 1;

    for(int i=1; i<=n; i++)
    {
       int index=1;
       double Min=oo;
       for(int j=1; j<=n; j++)
       {
           if(!vis[j] && dist[j]<Min)
           {
               Min = dist[j];
               index = j;
           }
       }

       if(index==1)
        continue;

       vis[index] = 1;
       ans += Min;

       for(int j=1; j<=n; j++)
       {
           if(!vis[j] && dist[j] > G[index][j])
           {
               dist[j] = G[index][j];
           }
       }
    }
    return ans;
}

int main()
{
    while(scanf("%d", &n)!=EOF)
    {
        for(int i=1; i<=n; i++)
            scanf("%lf%lf", &s[i].x, &s[i].y);

        for(int i=1; i<=n; i++)
        for(int j=1; j<=i; j++)
            G[i][j] = G[j][i] = sqrt((s[i].x-s[j].x)*(s[i].x-s[j].x)+(s[i].y-s[j].y)*(s[i].y-s[j].y) );

        printf("%.2f\n", prim());
    }
    return 0;
}