kuangbin_MST C (POJ 2031)

#include <cstdio>
#include <cmath>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>
#define INF 0x3F3F3F3F
using namespace std;

struct Node{double x, y, z, r;}node[110];

typedef pair<double, int> pdi;
struct cmp{
    bool operator () (const pdi a, const pdi b){
        return a.first > b.first;
    }
};

double val[110][110];

double nodeDist(Node a, Node b){
    return max(0.0, 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)) - a.r - b.r);
}

double prim(int n, int s)
{
    double ans = 0, dist[110];
    bool vis[110];
    memset(vis, false, sizeof vis);
    priority_queue<pdi, vector<pdi>, cmp> q;
    
    for(int i = 1; i <= n; i++){
        dist[i] = val[s][i];
        q.push(make_pair(dist[i], i));
    }
    vis[s] = true;
    while(!q.empty()){
        pdi u = q.top();
        q.pop();
        if(vis[u.second]) continue;
        vis[u.second] = true;
        ans += u.first;
        for(int i = 1; i <= n; i++){
            if(!vis[i] && dist[i] > val[u.second][i]){
                dist[i] = val[u.second][i];
                q.push(make_pair(dist[i], i));
            }
        }
    }
    return ans;
}

int main()
{
    int n;
    while(scanf("%d", &n), n){
        for(int i = 1; i <= n; i++){
            scanf("%lf%lf%lf%lf", &node[i].x, &node[i].y, &node[i].z, &node[i].r);
            for(int j = 1; j <= i; j++){
                val[i][j] = val[j][i] = nodeDist(node[i], node[j]);
            }
        }
        printf("%.3f\n", prim(n, 1));
    }
    return 0;
}