Minimum Add to Make Parentheses Valid

min_add_to_make_valid.rb

# @param {String} s
# @return {Integer}
def min_add_to_make_valid(s)
  res     = 0
  balance = 0

  s.each_char do |c|
    balance +=  c == '(' ? 1 : -1

    if balance < 0
      res += 1
      balance += 1
    end
  end

  res + balance
end