最小生成树prim算法 POJ2031

#include<iostream>
#include<algorithm>
#include<string.h>
#include<ctype.h>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<limits.h>
#include<queue>
#include<stack>
using namespace std;
#define INF 0xfffffff
#define max(a, b) a>b?a:b;
#define min(a, b) a<b?a:b;
const int N=110;
struct node
{
    double x, y, z, r;
} maps[N];
int visit[N];
double p[N][N], dist[N];
double solve(node a, node b)
{
    double s, d;
    d=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z));
    s=d-a.r-b.r;
    if(s<0)
        s=0.000;
    return s;
}
void prim(int n)
{
    int i, j, index;
    double ans;
    for(i=0; i<n; i++)
        dist[i]=p[0][i];
    visit[0]=1;
    for(i=1; i<n; i++)
    {
        double Min=INF;
        for(j=0; j<n; j++)
        {
            if(!visit[j]&&dist[j]<Min)
            {
                index=j;
                Min=dist[j];
            }
        }
        ans+=Min;
        visit[index]=1;
        for(j=0; j<n; j++)
        {
            if(!visit[j]&&dist[j]>p[index][j])
                dist[j]=p[index][j];
        }
    }
    printf("%.3lf\n", ans);
}
int main()
{
    int n, i, j;
    while(scanf("%d", &n), n)
    {
        memset(p, 0, sizeof(p));
        memset(visit, 0, sizeof(visit));
        memset(maps, 0, sizeof(maps));
        for(i=0; i<n; i++)
            scanf("%lf%lf%lf%lf", &maps[i].x, &maps[i].y, &maps[i].z, &maps[i].r);
        for(i=0; i<n; i++)
        {
            for(j=0; j<=i; j++)
            {
                p[i][j]=p[j][i]=solve(maps[i], maps[j]);
            }
        }
        prim(n);
    }
    return 0;
}