poj2031

简单题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define maxn 105
#define eps 10E-9
#define inf 10000000

struct Point
{
    double x, y, z, r;
} point[maxn];

double g[maxn][maxn];
int vis[maxn], n;
double lowc[maxn];

double dis(Point &a, Point &b)
{
    Point c;
    c.x = abs(a.x - b.x);
    c.y = abs(a.y - b.y);
    c.z = abs(a.z - b.z);
    double ret = sqrt(c.x * c.x + c.y * c.y + c.z * c.z);
    if (ret > a.r + b.r + eps)
        return ret - a.r - b.r;
    return 0;
}

void input()
{
    for (int i = 0; i < n; i++)
        scanf("%lf%lf%lf%lf", &point[i].x, &point[i].y, &point[i].z,
                &point[i].r);
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            g[i][j] = dis(point[i], point[j]);
}

double prim(double cost[][maxn], int n)
{
    int i, j, p;
    double minc, res = 0;
    memset(vis, 0, sizeof(vis));
    vis[0] = 1;
    for (i = 1; i < n; i++)
        lowc[i] = cost[0][i];
    for (i = 1; i < n; i++)
    {
        minc = inf;
        p = -1;
        for (j = 0; j < n; j++)
            if (0 == vis[j] && minc > lowc[j])
            {
                minc = lowc[j];
                p = j;
            }
        if (inf == minc)
            return -1;
        res += minc;
        vis[p] = 1;
        for (j = 0; j < n; j++)
            if (0 == vis[j] && lowc[j] > cost[p][j])
                lowc[j] = cost[p][j];
    }
    return res;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d", &n), n)
    {
        input();
        double ans = prim(g, n);
        printf("%.3f\n", ans);
    }
    return 0;
}