Task:

 Generate a string with   N   opening brackets   [   and with   N   closing brackets   ],   in some arbitrary order. 
 Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.


Examples

   (empty)      OK
   []           OK   
   [][]         OK   
   [[][]]       OK 
   ][         NOT OK
   ][][       NOT OK
   []][[]     NOT OK



def generate(n : Int) 
  (['[',']'] * n).shuffle.join # Implicit return
end
 
def is_balanced(str : String)
  count = 0
  str.each_char do |ch|
    case ch
    when '['
      count += 1
    when ']'
      count -= 1
      if count < 0
        return false
      end
    else
      return false
    end
  end
  count == 0
end
 
10.times do |i|
  str = generate(i)
  puts "#{str}: #{is_balanced(str)}"
end