BZOJ 1975 魔法猪学院（K短路）

vector<pair<int,double> > g[N],g1[N];
double dis[N];
int n,m;
double Sum;


struct node
{
    int v;
    double dis;
    
    node(){}
    node(int _v,double _dis)
    {
        v=_v;
        dis=_dis;
    }
    
    int operator<(const node &a) const
    {
        return dis>a.dis;
    }
};


int inq[N];


void SPFA()
{
    int i;
    FOR1(i,n) dis[i]=dinf;
    dis[n]=0; inq[n]=1;
    queue<int> Q;
    Q.push(n);
    int u,v;
    double w;
    while(!Q.empty())
    {
        u=Q.front();
        Q.pop();
        
        inq[u]=0;
        FOR0(i,SZ(g1[u]))
        {
            v=g1[u][i].first;
            w=g1[u][i].second;
            if(dis[v]>dis[u]+w)
            {
                dis[v]=dis[u]+w;
                if(!inq[v]) inq[v]=1,Q.push(v);
            }
        }
    }
}




priority_queue<node> Q;


int cal()
{
    Q.push(node(1,dis[1]));
    int ans=0,i,v;
    node p;
    double w;
    while(!Q.empty())
    {
        p=Q.top();
        Q.pop();
        
        if(p.dis>Sum+EPS) break;
        
        if(p.v==n) 
        {
            ans++;
            Sum-=p.dis;
            continue;
        }
        FOR0(i,SZ(g[p.v]))
        {
            v=g[p.v][i].first;
            w=g[p.v][i].second;
            Q.push(node(v,p.dis-dis[p.v]+w+dis[v]));
        }
    }
    return ans;
}


int main()
{
    RD(n,m); RD(Sum);
    int i,u,v;
    double w;
    FOR1(i,m)
    {
        RD(u,v);RD(w);
        g[u].pb(MP(v,w));
        g1[v].pb(MP(u,w));
    }
    SPFA();
    PR(cal());
}