gistfile1.rb

# zad5 http://dl-client3.getdropbox.com/u/70986/infa/matura2007/inf_pr_cz2.pdf

class Fixnum
  def first?
    !(2..Math.sqrt(self)).any? {|i| self % i == 0}
  end
  
  def sum_is_first?
    self.to_s.split(//).inject(0) {|s, e| s+=e.to_i}.first?
  end
  
  def binary_sum_is_first?
    self.to_s(2).split(//).inject(0) {|s, e| s+=e.to_i}.first?
  end
  
  def super_first?
    first? && sum_is_first?
  end
  
  def super_b_first?
    super_first? && binary_sum_is_first?
  end
end

puts "a)"
[(2..1000), (100..10000), (1000..100000)].each do |range|
  puts "   #{range} => #{range.reject{|e| !e.super_b_first?}.size}"
end

puts "b) " + (100..10000).reject{|e| !e.sum_is_first?}.size.to_s

sum = (100..10000).reject{|e| !e.super_b_first?}.inject(0){|s, e| s+=e}
puts "c) #{sum} => #{sum.first?}"

# a)
#    2..1000 => 51
#    100..10000 => 249
#    1000..100000 => 1262
# b) 2976
# c) 1006623 => false