1時間以内に解けなければプログラマ失格となってしまう5つの問題 ref: http://qiita.com/pocari/items/8b9f6b31dfe551e39693

file0.txt

echo 5 2 1 9 50 56 | ruby -e "puts gets.split(/\s+/).permutation.map(&:join).max"

file1.txt

def gen_pattern(depth, size, acc = [])
  if depth >= size
    exp = (1 .. (size + 1)).zip(acc).flatten.join.gsub(/ /, "").gsub(/(\+|-)/, ' \1 ')
    puts exp if eval(exp) == 100
  else
    [" ", "+", "-"].each do |op|
      gen_pattern(depth + 1, size, acc + [op])
    end
  end
end

gen_pattern(0, 8)

file2.txt

puts [" ", "+", "-"].repeated_permutation(8).map{|e|
  (1 .. 9).zip(e).flatten.join.gsub(/ /, '').gsub(/(\+|-)/, ' \1 ')
}.select {|e|
  eval(e) == 100
}

file3.txt

[["1", "2", ["3"]], ["4", "5"]].join
#=> "12345"

file4.txt

irb(main):001:0> ary = [1, 2, 3]
=> [1, 2, 3]
irb(main):002:0> ary[0] = ary
=> [[...], 2, 3]

file5.txt

irb(main):003:0> ary[0][1]
=> 2
irb(main):004:0> ary[0][0][1]
=> 2
irb(main):005:0> ary[0][0][0][1]
=> 2
irb(main):006:0> ary.join
ArgumentError: recursive array join
        from (irb):6:in `join'
        from (irb):6
        from D:/Ruby21-x64/bin/irb:11:in `<main>'

file6.txt

puts [" ", "+", "-"].repeated_permutation(8).map{|e|
  (1 .. 9).zip(e).join.gsub(/ /, '').gsub(/(\+|-)/, ' \1 ')
}.select {|e|
  eval(e) == 100
}