題目要求基本如下：
請編寫一個控制臺程序,要求用戶可以輸入任意組條件，定義兩個字母之間的大小關系。程序可以通過已輸入的條件，推斷出給定的兩個字母之間的大小關系。例如：
用戶輸入：A>B
用戶輸入：B>C
用戶輸入：A?C
程序顯示：A>C
用戶輸入：C<D
用戶輸入：A?D
程序顯示：無法判斷
用戶輸入：A<C
程序顯示：與原有條件沖突



#include <cstdlib>
#include <iostream>

using namespace std;
/*
*數組依次存放A-Z,并保存大于和小于該字母的字母鏈表
*/
const int N = 26;
struct CharNode
{
       CharNode( char n,CharNode* p):node(n),next(p){}
       
       char node;
       CharNode* next;
};
struct ArrayNode
{
       int sign;
       CharNode* up;
       CharNode* down;
};

ArrayNode array[N];

void Init( )
{
     for ( int i = 0; i < N; ++i )
     {
         array[i].sign = 0;
         array[i].up = NULL;
         array[i].down = NULL;
     }
};

void Free( )
{
     CharNode* pChar = NULL;
     for ( int i = 0; i < N; ++i )
     {
         pChar = array[i].up;
         while( NULL != pChar )
         {
                array[i].up = pChar->next;
                delete pChar;
                pChar = array[i].up;
         }
         pChar = array[i].down;
         while( NULL != pChar )
         {
                array[i].down = pChar->next;
                delete pChar;
                pChar = array[i].down; 
         }
     }
};

void Reset( )
{
     for ( int i = 0; i < N; ++i )
     array[i].sign = 0;
};




void InsertNodeUp( char arraynode, char c )
{
     CharNode* pNode = new CharNode(c,NULL);
     CharNode* pCharNode = array[arraynode-'A'].up;
     if ( NULL != pCharNode )
          pNode->next = pCharNode;
         
     array[arraynode-'A'].up = pNode; 
 
};
void InsertNodeDown( char arraynode, char c )
{
     CharNode* pNode = new CharNode(c,NULL);
     CharNode* pCharNode = array[arraynode-'A'].down;
     if ( NULL != pCharNode )
          pNode->next = pCharNode;
         
     array[arraynode-'A'].down = pNode;  
};




bool _FindUp(  char source, char dest )
{
     if ( source == dest )
        return true;
    
     if ( 1 == array[source-'A'].sign )
        return false;  

     array[source-'A'].sign = 1;
    
     CharNode* pChar = array[source-'A'].up;
   
     while ( NULL != pChar )
     {
           if ( _FindUp(pChar->node,dest) )
           return true;
           pChar = pChar->next;
     }
     return false;
};
bool FindUp( char source, char dest )
{
     Reset( );
     return _FindUp(source,dest);
};



bool _FindDown( char source, char dest )
{   
     if ( source == dest )
     return true;
    
     if ( 1 == array[source-'A'].sign )
     return false;  
     array[source-'A'].sign = 1;
    
     CharNode* pChar = array[source-'A'].down;   
     while ( NULL != pChar )
     {
           if ( _FindDown(pChar->node,dest) )
           return true;
           pChar = pChar->next;
     }
     return false;
};
bool FindDown( char source, char dest )
{
     Reset( );
     return _FindDown(source,dest);
};


int main(int argc, char *argv[])
{
    char first;
    char compare;
    char second;
    char minchar;
     
    Init( );
   
    while( 1 )
    {
           cin >> first >> compare >> second;
           minchar = first < second ? first:second;
           switch( compare )
           {
                 case '>':
                 if ( FindUp(first,second) )
                 {
                     cout << "Wrong" << endl;  
                     break; 
                 }
        
                 InsertNodeDown(first,second);
                 InsertNodeUp(second,first);                    
                 break;
                                    
                 case '<':                     
                 if ( FindDown(first,second) )
                 {
                      cout << "Wrong" << endl;
                      break;
                 }                                   

                 InsertNodeUp( first,second );
                 InsertNodeDown( second,first );             
                 break;
                       
                 case '?':
                 if ( FindUp(first,second) )
                 {
                      cout <<first<<'<'<<second<<endl;
                      break;
                 }
                 if( FindDown(first,second) )
                 {
                        cout<<first<<'>'<<second<<endl;
                        break;
                 }
                 cout << "Unknown" << endl;   
                 break;
                   
                 case 'Q':
                 goto End;             
           }        
    }
 
 End:  
    Free( );
   
    system("PAUSE");
    return EXIT_SUCCESS;
}