poj2031

简单题

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#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;
}