bigger_same_digits.rb

require 'set'

def possible?(n)
  if n.to_s == n.to_s.chars.sort.reverse.join then false else true end
end

def same_digits?(a1, a2)
  if Set.new(a1.to_s.chars) == Set.new(a2.to_s.chars) then true else false end
end

# puts possible?(4321) # false 
# puts possible?(4231) # true

def next_bigger(n)
  res = nil
  if possible?(n) then
    n.upto(Float::INFINITY) { |num| if same_digits?(n, num) && possible?(num)
                                    then num 
                                    else nil end }
    end
end

puts next_bigger(4231) # should be 4321