USACO 3.3 Riding The Fences

USACO 3.3 Riding The Fences

欧拉回路问题，只要每次按编号从小到大找边，最后逆序输出欧拉路径即可。

#include  < iostream >
#include  < fstream >
#include  < stack >

using   namespace  std;

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

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

int  graph[ 501 ][ 501 ];
int  degree[ 501 ];
int  odd_degree_node[ 2 ];
int  max_vertex  =  INT_MIN;
int  min_vertex  =  INT_MAX;

int  euler_path[ 1025 ];
int  path_cnt;

void  find_path( int  vertex)
{
    stack < int > s;
     int  t;

    s.push(vertex);

     while (  ! s.empty() ){
        t  =  s.top();      
         if (degree[t] == 0 ){
            euler_path[path_cnt ++ ]  =  t;
            s.pop();
             continue ;
        }

         for ( int  i = min_vertex;i <= max_vertex; ++ i){
             if ( graph[t][i] ){
                graph[t][i] -- ;
                graph[i][t] -- ;
                degree[t] -- ;
                degree[i] -- ;
                s.push(i);
                 break ;
            }
        }
    }
}

void  solve()
{
     int  f;
     in >> f;

     int  a,b;
     while (f -- ){
         in >> a >> b;
        graph[a][b] ++ ;
        graph[b][a] ++ ;
        degree[a] ++ ;
        degree[b] ++ ;
        max_vertex  =  max(max_vertex,max(a,b));
        min_vertex  =  min(min_vertex,min(a,b));
    }

     int  odd_degree_cnt  =   0 ;
     for ( int  i = min_vertex;i <= max_vertex; ++ i){
         if (degree[i] & 1 ){
            odd_degree_node[odd_degree_cnt ++ ]  =  i;
        }
    }

     int  start  =  min_vertex;
     if ( odd_degree_cnt != 0 ){
        start  =  odd_degree_node[ 0 ];
    }

    find_path(start);

     for ( int  i = path_cnt - 1 ;i >= 0 ; -- i)
         out << euler_path[i] << endl;
}

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