舞蹈链变种，估价函数，选择一个未被控制的列，很明显该列最少需要1个行来控制，所以我把ret++。该列被控制后，我把它所对应的行，全部设为已经选择，并把这些行对应的列也设为被控制。继续选择未被控制的列，直到没有这样的列。-The dance chain variants, the valuation function, select a column not control, it is clear that column requires a minimum of a line of control, the I ret++. The column control to the corresponding row, all set to have chosen, and the corresponding column of these rows is also set to be controlled. The continue selecting Uncontrolled column is, until no such a column.