class GenString
    def initialize(n)
        @a = Array.new(n)
    end

    def binString(n)
        if n < 1
            @a.each_slice(3) { |a,b,c| puts [c,b,a]*'  ' }
        else
            @a[n-1] = 0
            binString(n-1)
            @a[n-1] = 1
            binString(n-1)
        end
    end
end

gen = GenString.new(3)
gen.binString(3)