TOKENS = { '}' => '{', ')' => '(', ']' => '[' }.freeze

def valid_brace?(input)
  stack = []
  valid = true

  input.each_char do |c|
    case c
    when '(', '[', '{' then stack.push(c)
    when ')', ']', '}' then valid = (stack.pop == TOKENS[c])
    else
      valid = false
    end

    break unless valid
  end

  valid && stack.empty?
end

inputs = ['()[]{}', '([{}])', '[({})](]', '[(])', '(}']

inputs.each do |input|
  text = valid_brace?(input) ? "valid" : "invalid"
  puts "#{input} is #{text}"
end