Solution.rb

# @param {String} s
# @return {Boolean}
def is_valid(s)
  stack = ''
  s.split('').each do |c|
    if ['{', '[', '('].include?(c)
      stack += c
    else
      if c == '}' && stack[stack.length - 1] == '{'

        stack = stack.length > 1 ? stack[0..stack.length - 2] : ""
      elsif c == ']' && stack[stack.length - 1] == '['
        stack = stack.length > 1 ? stack[0..stack.length - 2] : ""
      elsif c == ')' && stack[stack.length - 1] == '('
        stack = stack.length > 1 ? stack[0..stack.length - 2] : ""
      else
        return false
      end
    end
  end
  stack == ''
end