# '(', '{', '[' are called "openers."
# ')', '}', ']' are called "closers."
# Write an efficient function that tells us whether or not an input string's openers and closers are properly nested.

# Examples:

# "{ [ ] ( ) }" should return True
# "{ [ ( ] ) }" should return False
# "{ [ }" should return False



def is_valid code
  openers_to_closers = {
        '(' => ')',
        '{' => '}',
        '[' => ']',
  }
  openers = openers_to_closers.keys
  closers = openers_to_closers.values
  openers_stack = []
  code.split('').each do |char|
    if openers.include? char
      openers_stack << char
    else
      if openers_stack.empty?
        return false
      else
        lastest_pushed_to_stack = openers_stack.pop()
        if !(openers_to_closers[lastest_pushed_to_stack] == char)
          return false
        end
      end
    end
  end
  return openers_stack == []
end