USACO 3.2 Sweet Butter

USACO 3.2 Sweet Butter

稀疏图的多源最短路径问题，用heap+disjktra解决。

#include  < iostream >
#include  < fstream >
#include  < list >
#include  < queue >

using   namespace  std;

ifstream fin( " butter.in " );
ofstream fout( " butter.out " );

#ifdef _DEBUG
#define  out cout
#define  in cin
#else
#define  out fout
#define  in fin
#endif

int  n,p,c;

struct  edge{
     int  node;
     int  weight;
    edge( int  n, int  w):node(n),weight(w){
    }
};

struct  graph_node{
   list < edge >  adj; 
};

struct  pri_que_node{
     int  num;
     int  dist;
    pri_que_node( int  n, int  d):num(n),dist(d){
    };
     bool   operator <  ( const  pri_que_node  & n2)  const {
         return  dist > n2.dist;
    }
};

graph_node graph[ 801 ];
int  cow_place[ 801 ];
int  shortest_path[ 801 ][ 801 ];

void  get_shortest( int  n)
{
     for ( int  i = 1 ;i < 801 ; ++ i)
        shortest_path[n][i]  =  INT_MAX;

    shortest_path[n][n]  =   0 ;
    priority_queue < pri_que_node >  pq;
     for (list < edge > ::iterator li  =  graph[n].adj.begin();
                   li != graph[n].adj.end();
                   li ++ ){
        pq.push( pri_que_node(li -> node,li -> weight) );
        shortest_path[n][li -> node]  =  li -> weight;
    }

     while (  ! pq.empty() ){
       pri_que_node node  =  pq.top();
       pq.pop();

        if ( node.dist >  shortest_path[n][node.num] )
            continue ;

       shortest_path[n][node.num]  =  node.dist;

        for (list < edge > ::iterator li  =  graph[node.num].adj.begin();
                   li != graph[node.num].adj.end();
                   li ++ ){
            if ( node.dist + li -> weight  <  shortest_path[n][li -> node] ){
               shortest_path[n][li -> node]  =  node.dist + li -> weight;
               pq.push( pri_que_node(li -> node, shortest_path[n][li -> node]) );
           }
        }
    }
}

void  solve()
{
     in >> n >> p >> c;

     for ( int  i = 0 ;i < n; ++ i)
         in >> cow_place[i];

     int  a,b,w;
     while (c -- ){
         in >> a >> b >> w;
        graph[a].adj.push_back( edge(b,w) );
        graph[b].adj.push_back( edge(a,w) );
    }
#ifdef _DEBUG
     for ( int  i = 1 ;i <= p; ++ i){
         if ( ! graph[i].adj.empty()){
            cout << " node: " << i << "   " ;
            for (list < edge > ::iterator li  =  graph[i].adj.begin();
                   li != graph[i].adj.end();
                   li ++ ){
               cout << " ( " << li -> node << " , " << li -> weight << " ) " ;
           }
           cout << endl;
        }
    }
#endif

     for ( int  i = 1 ;i <= p; ++ i)
        get_shortest(i);

     int  res  =  INT_MAX;

     for ( int  i = 1 ;i <= p; ++ i){
         int  t  =   0 ;
         for ( int  j = 0 ;j < n; ++ j){
            t +=  shortest_path[i][cow_place[j]];
        }
        res  =  min(res,t);
    }

     out << res << endl;

}

int  main( int  argc, char   * argv[])
{
    solve(); 
     return   0 ;
}