paren balancing

balance.rb

# Balanced paren strings have the property that each opening ( has a closing ).
# This proceeds by scanning left to right, using a stack to keep track of open 
# parens.
def balanced?(string)
  characters = string.split(//)
  stack = []
  characters.each do |c|
    stack.push(c) if c == "(" 

    return false if stack.empty? and c == ")"
    stack.pop if c == ")"
  end
  return stack.empty?
end

["()", "()()", "(()(()))", "()()()", "((((()))))", 
  ")", "()(()", "(()))", "((((())))", "(()()))"].each do |s|
  puts "#{s} : #{balanced?(s)}"
end