Ruby bracket matching using stack

bracket_matching.rb

class BracketDemo
    def solution(str)
        valid = true
        stack = []

        str.each_char do |char|
            case char
            when '[', '{', '('
                stack.push(char)
            when ']'
                last = stack.pop
                valid = false if last != '['
            when ')'
                last = stack.pop
                valid = false if last != '('
            when '}'
                last = stack.pop
                valid = false if last != '{'
            end
        end

        valid && stack.empty? ? 1 : 0
    end
end


puts BracketDemo.new.solution("[]}()")
puts BracketDemo.new.solution("[]{}()")