check_brackets.rb

def brackets_valid?(str)
  open = []
  matches = { '{' => '}', '(' => ')', '[' => ']' }
  str.split('').each do |c|
    if matches.keys.include? c # it's an opening bracket
      open.push c
    elsif matches.values.include? c # it's a closing bracket
      # must close the last open bracket
      return false unless c == matches[open.pop]
    end
  end
  true
end

def check(str)
  puts brackets_valid?(str) ? "Valid" : "Invalid"
end

check("{}")
check("{{)")
check("{ code goes here }")