POJ-2031 最小生成树

https://vjudge.net/problem/POJ-2031

#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<cmath>
#include<cstdio>
#define mem(s,value) memset(s,value,sizeof(s))
#define frein(s)  freopen(s,"r",stdin)
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
const int maxn = 400;

class Point{
public:
    double x,y,z,r;
    Point(){};
    Point(double x_,double y_,double z_,double r_):x(x_),y(y_),z(z_),r(r_){};
    double operator- (const Point& rhs)const{
        double s = (x-rhs.x)*(x-rhs.x)+(y-rhs.y)*(y-rhs.y)+(z-rhs.z)*(z-rhs.z);
        double d = (r+rhs.r)*(r+rhs.r);
        double p = s - d;
        return p<=0? 0 : sqrt(s)-sqrt(d);
    }
};

Point all[maxn];
double mapper[maxn][maxn];
int n;

int readin(){
    scanf("%d",&n);
    if(!n)return 0;
    //初始化数组
    mem(mapper,0);
    //开始读入
    for(int i=0;i<n;i++){
        double x,y,z,r;
        cin>>x>>y>>z>>r;
        all[i] = Point(x,y,z,r);
        for(int k=0;k<i;k++){
            //更新不同的点之间的距离
            mapper[i][k] = mapper[k][i] = (all[i]-all[k]);
        }
        mapper[i][i]=0;
    }
    return 1;
}

double dis[maxn];
int vis[maxn];
double Value;
int solve(){
    Value = 0;
    mem(vis,0);
    vis[0]=1;
    for(int i=0;i<n;i++)dis[i]=mapper[0][i];
    //
    for(int i=1;i<n;i++){
        double minc=0x3f3f3f3f;
        int p = -1;
        for(int k=0;k<n;k++){
            if(!vis[k] && minc>dis[k]){
                minc = dis[k];
                p = k;
            }
        }
        Value += minc;
        vis[p] = 1;
        for(int k=0;k<n;k++){
            dis[k] = min(dis[k],mapper[p][k]);
        }
    }
    printf("%.3lf\n",Value);
    return 0;
}

int main(){
    //frein("in.txt");
    while(readin()){
        solve();
        //break;
    }
    return 0;
}

//https://vjudge.net/problem/POJ-2031

OK