http://www.softantenna.com/wp/software/5-programming-problems/ の問題5

5.rb

def formula_ptn(ptn)
  ope = ptn.to_s(3).rjust(8, '0').gsub('0', 'n').gsub('1', '+').gsub('2', '-')
  (1..9).map(&:to_s).each_with_index.inject('') do |result, (num, index)|
    result += num
    if ope[index] && ope[index] != 'n'
      result += ope[index]
    end
    result
  end
end

0.upto('22222222'.to_i(3)) do |ptn|
  f = formula_ptn(ptn)
  puts f if eval(f) == 100
end

# 123+45-67+8-9
# 123+4-5+67-89
# 123-45-67+89
# 123-4-5-6-7+8-9
# 12+3+4+5-6-7+89
# 12+3-4+5+67+8+9
# 12-3-4+5-6+7+89
# 1+23-4+56+7+8+9
# 1+23-4+5+6+78-9
# 1+2+34-5+67-8+9
# 1+2+3-4+5+6+78+9