poj 1094 Sorting It All Out Folyd+dfs拓扑排序

poj 1094 Sorting It All Out Folyd+dfs拓扑排序

每接受一组关系，用Floyd算法计算传递闭包，

判断是否有矛盾：if(adj[i][j]&&adj[j][i])isInconsitent=true;

判断是否有关系未确定：if(adj[i][j]==0&&adj[j][i]==0&&(i!=j))issorted=false;

如果没有矛盾，所以关系确定，则说明已经sort好了，用dfs拓扑排序输出即可。

然后把未接受的数据接受完，刚开始直接跳出了。

#include < iostream >
#include < cstring >
#include < vector >
using   namespace  std;
bool  adj[ 27 ][ 27 ];  int  n,m;
bool  visit[ 27 ],isInconsitent = false ,issorted = true ;
vector < int > vec;
void  Floyd()
{
     int  i,j,k;
     for (k = 1 ; k <= n; k ++ )
         for (i = 1 ; i <= n; i ++ )
             for (j = 1 ; j <= n; j ++ )
                 adj[i][j] =  (adj[i][j] || adj[i][k] && adj[k][j]);
}

void  check()
{
    isInconsitent = false ,issorted = true ;
     int  i,j;
     for (i = 1 ; i <= n; i ++ )
         for (j = 1 ; j <= n; j ++ )
        {
             if (adj[i][j] && adj[j][i])isInconsitent = true ;
             if (adj[i][j] == 0 && adj[j][i] == 0 && (i != j))issorted = false ;
        }
}

void  dfs( int  i)
{
    visit[i] = true ;
     for ( int  j = 1 ; j <= n; j ++ )
         if ( ! visit[j] && adj[i][j])
            dfs(j);
    vec.push_back(i);
}
int  main()
{
     while (cin >> n >> m)
    {
         if (n == 0 && m == 0 ) break ;
        memset(adj, 0 , sizeof  adj);
         bool  print = false ;
         int  i,j;
         char  pre,last,less;
         for (i = 1 ; i <= m; i ++ )
        {
            cin >> pre >> less >> last;
            adj[ int (pre - ' A ' + 1 )][ int (last - ' A ' + 1 )] = true ;
            
            Floyd();

            check();
            
             if (isInconsitent)
            {
                cout << " Inconsistency found after  " << i << "  relations. " << endl;
                print  = true ;  break ;
            }

             if (issorted)
            {
                cout << " Sorted sequence determined after  " << i << "  relations:  " ;
                vec.clear();
                memset(visit, 0 , sizeof  visit); 
                 for ( int  t = 1 ; t <= n; t ++ )
                     if ( ! visit[t])dfs(t); 
                 while (vec.size())
                {
                    cout << char (vec[vec.size() - 1 ] + ' A ' - 1 );
                    vec.pop_back(); 
                }
                cout << ' . ' << endl;
                print = true ;  break ;
            }
            
        }
         if (print == false )cout << " Sorted sequence cannot be determined. " << endl;
         // accept the data left
         for (j = i + 1 ; j <= m; j ++ )
            cin >> pre >> less >> last;
    }

     return   0 ;
}