def is_balanced?(string)
  stack = []
  string.chars.each do |char|
    case char
      when '('
        stack.push '('
      when ')'
        if stack.empty? || stack.pop != '('
          return false
        end
    end
  end
  stack.empty?
end

data = [
  "a+(b*c)-2-a",
  "(a+b*(2-c)-2+a)*2",
  "(a*b-(2+c)",
  "2*(3-a))",
  ")3+b*(2-c)("
]

data.each do |string|
  puts "#{string}:  #{is_balanced?(string)}"
end