private ColumnNode ChooseNextColumn()
{
Contract.Assume(!(_root is null));
int size = int.MaxValue;
var nextColumn = new ColumnNode(-1);
var j = _root.Right.Column;
while (j != _root)
{
Contract.Assert(!(j is null));
if (j.Size < size)
{
nextColumn = j;
size = j.Size;
}
j = j.Right.Column;
}
return(nextColumn);
}
public DancingLink(ColumnNode root) => Root = root;