プログラマ脳を鍛える数学パズル：Q02

puzzle02.rb

# -- 処理時間計測の自作ライブラリ --
require './process_measure.rb'
# ------------------------------

def print_enable_combinarion(from, to)
  (from..to).each do |num|
    nums = num.to_s.split('')
    puts num if enable_combinarion?(nums)
  end
end

def enable_combinarion?(nums)
  combi(nums).each do |f|
    # この辺のガードが苦しいし無駄....
    next if f =~ /0[1-9]/
    next if f =~ /\/0/
    next if f !~ /[\+\-\*\/]/
    return true if eval(f).to_s == (nums.join('')).reverse
  end
  return false
end

def combi(a)
  res_array = [a[0]]
  res_array = add_sign_and_num(res_array, a[1])
  res_array = add_sign_and_num(res_array, a[2])
  res_array = add_sign_and_num(res_array, a[3])
  res_array
end

def add_sign_and_num(a, num)
  a.product(["+", "-", "*", "/", ""]).map {|m| "#{m.join('')}#{num}" }
end

measure_do { print_enable_combinarion(1000, 9999) }