/* ECP: FILEname=fig11_25.c */
/* 1*/   /* Same As ChooseMove, But Use Alpha Beta Pruning. */

/* 2*/   int
/* 3*/   Choose( BoardType B, Side S, int *BestRow, int *BestColumn,
/* 4*/           int Alpha, int Beta )
/* 5*/   {

/*14*/           /* Up To Here, Everything Is Identical... */
/*15*/           /* Set Some Variables Depending On Who S Is */
/*16*/       if( S == Me )
/*17*/       {
/*18*/           Opp = You; Value = Alpha; Mypiece = Computer;
/*19*/       }
/*20*/       else
/*21*/       {
/*22*/           Opp = Me; Value = Beta; Mypiece = Human;
/*23*/       }

/*24*/           /* Search for A Move */
/*25*/       for( Row = 0; Row < Bsize; Row++ )
/*26*/           for( Column = 0; Column < Bsize; Column++ )
/*27*/               if( IsEmpty( B, Row, Column ) )
/*28*/               {
/*29*/                   Place( B, Row, Column, Mypiece );
/*30*/                   if( S == Me )
/*31*/                   {
/*32*/                       Reply = Choose( B, Opp, &Z, &Z, Value, Beta );
/*33*/                       Unplace( B, Row, Column );
/*34*/                       if( Reply > Value )
/*35*/                       {
/*36*/                           *BestRow = Row; *BestColumn = Column;
/*37*/                           if( ( Value = Reply ) >= Beta )
/*38*/                               return Value;  /* Refutation Found */
/*39*/                       }
/*40*/                   }
/*41*/                   else
/*42*/                   {
/*43*/                       Reply = Choose( B, Opp, &Z, &Z, Alpha, Value );
/*44*/                       Unplace( B, Row, Column );
/*45*/                       if( Reply < Value )
/*46*/                       {
/*47*/                           *BestRow = Row; *BestColumn = Column;
/*48*/                           if( ( Value = Reply ) <= Alpha )
/*49*/                               return Value;  /* Refutation Found */
/*50*/                       }
/*51*/                   }
/*52*/               }

/*53*/       return Value;
/*54*/   }