Jarnik-Prim

//F means for!
#define MX 128
struct nd{
    nd(int a,double w):t(a),w(w){};
    int t;
    double w;
    bool operator<(const nd&r)const{return w>r.w;}
};
int cn[MX],N,m;
double g[MX][MX];
double spt(void){
    double S(0);
    memset(cn,0,sizeof(cn));
    cn[0]=1;
    priority_queue<nd> q;
    for(int i(1);i<N;++i)
        q.push(nd(i,g[0][i]));
    while(!q.empty()){
        S+=q.top().w;
        int a(q.top().t);
        cn[a]=1;
        F(N)q.push(nd(i,g[a][i]));
        while(!q.empty()&&cn[q.top().t])
            q.pop();
    }
    return S;
}