八皇后问题（递归版）

/**
 *  @author  phinecos
 *  @since  2008/10/31
  */
class  EightQueen
{ 
     static   final   int  MAXSIZE  =   8 ; // 棋盘大小
     static   int  okTimes  =   0 ;  // 解法个数
     static   int [][] chess  =   new   int [MAXSIZE][MAXSIZE]; // 棋盘

     public   static   boolean  CanPut( int  row, int  col)
    { // 皇后能否放置在chess[row][col]的位置上
         // 第row行不能有多于1个皇后
         int  i,j;
         for (i = 0 ;i < MAXSIZE; ++ i)
        {
             if (chess[row][i] == 1 )
                 return   false ;
        }
         // 第col列不能有多于1个皇后
         for (i = 0 ;i < MAXSIZE; ++ i)
        {
             if (chess[i][col] == 1 )
                 return   false ;
        }
         // 对角线不能有多于1个皇后
         // 反对角线
         for (i = row - 1 ,j = col + 1 ;i >= 0 && j < MAXSIZE; -- i, ++ j)
        { 
             if (chess[i][j] == 1 )
                 return   false ;
        }
         for (i = row + 1 ,j = col - 1 ;i < MAXSIZE && j >= 0 ; ++ i, -- j)
        {
             if (chess[i][j] == 1 )
                 return   false ;
        }    
         // 对角线
         for (i = row - 1 ,j = col - 1 ;i >= 0 && j >= 0 ; -- i, -- j)
        {
             if (chess[i][j] == 1 )
                 return   false ;
        }
         for (i = row + 1 ,j = col + 1 ;i < MAXSIZE && j < MAXSIZE; ++ i, ++ j)
        {
             if (chess[i][j] == 1 )
                 return   false ;
        }
         return   true ;
    }
     public   static   void  Solve( int  curChess, int  num)
    {
         if (num == 8 )
        { // 八个皇后了，
            okTimes ++ ;
             return ;
        }
         else
        {
             if (curChess < 64 )
            {
                 int  i,j;
                i = curChess / MAXSIZE; // 行
                j = curChess % MAXSIZE; // 列
                 if (chess[i][j] == 0 && CanPut(i,j) == true )
                { // chesss[i][j]空着，并且经测试可以放置
                    chess[i][j] = 1 ;  // 放置皇后下去
                    Solve(curChess + 1 ,num + 1 );
                    chess[i][j] = 0 ;  // 回溯
                }
                Solve(curChess + 1 ,num);  // chess[i][j]无法放置，跳过它
            }
        }
    }
     public   static   void  main(String args[])
    { 
         int  i,j;
         for (i = 0 ;i < MAXSIZE; ++ i)
             for (j = 0 ;j < MAXSIZE; ++ j)
            {
                chess[i][j]  =   0 ;
            }
        Solve( 0 , 0 );
        System.out.println( " 八皇后问题共有 " + okTimes + " 个解法 " ); 
    }
}