From: James Edward Gray II <james@...>
Date: 2007-12-03T01:45:52+09:00
Subject: Fwd: Please Forward: Ruby Quiz Submission

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Begin forwarded message:

> From: Daniel Lindsley <daniel@snow-wolf.net>
> Date: December 1, 2007 12:53:48 AM CST
> To: submission@rubyquiz.com
> Subject: Please Forward: Ruby Quiz Submission
>
> James,
>
>
> 	I have a submission for Ruby Quiz #148: "Postfix to Infix".  It is  
> neither amazing nor beautiful but it seems to work and I've hit my  
> limit on time I can spend on it.  I'd appreciate any feedback if  
> it's appropriate to request it.  And my apologies if a different  
> packaging format or different means of bundling the code together  
> is preferred (I'm rather new to all of this).  Thank you for the  
> excellent site and challenges!
>
>
> Daniel
>
>

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class PostfixToInfix
  OPERATORS = %w{* / + -}
  
  def initialize(postfix)
    raise "Requires a postfix expression as a string." unless postfix.class == String
    raise "Requires a valid postfix expression." unless postfix.split.length >= 3
    @postfix = postfix
  end
  
  def convert(verbose=true)
    postfix_terms = @postfix.split
    
    if verbose
      convert_verbose(postfix_terms)
    else
      raise NotImplementedError("Because I'm pressed for time.")
    end
  end
  
  def convert_verbose(postfix_terms)
    infix_terms = []
    
    while not postfix_terms.empty?
      current_term = postfix_terms.shift
      
      if OPERATORS.include? current_term
        # Perform the old switcheroo.
        right = infix_terms.pop
        left = infix_terms.pop
        current_term = "(#{left} #{current_term} #{right})"
      end
      
      infix_terms.push current_term
    end
    
    return infix_terms.shift
  end
end

if __FILE__ == $0
  unless ARGV.length == 1
    puts "Usage: #{$PROGRAM_NAME} <postfix_string>"
    exit
  end
  
  ps2i = PostfixToInfix.new(ARGV.shift)
  puts ps2i.convert
end
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require 'test/unit'
require 'postfix_to_infix'

class PostfixToInfixTest < Test::Unit::TestCase
  VALID_CASES = [
    # { :postfix => '', :infix_verbose => '', :infix_preferred => '' }
    { :postfix => '2 3 -', :infix_verbose => '(2 - 3)', :infix_preferred => '2 - 3' },
    { :postfix => '2 3 5 + *', :infix_verbose => '(2 * (3 + 5))', :infix_preferred => '2 * (3 + 5)' },
    { :postfix => '56 34 213.7 + * 678 -', :infix_verbose => '((56 * (34 + 213.7)) - 678)', :infix_preferred => '56 * (34 + 213.7) - 678' },
    { :postfix => '1 56 35 + 16 9 - / +', :infix_verbose => '(1 + ((56 + 35) / (16 - 9)))', :infix_preferred => '1 + (56 + 35) / (16 - 9)' },
  ]
  
  def test_initialize_without_parameter_should_raise_exception
    assert_raise(ArgumentError) { PostfixToInfix.new }
  end
  
  def test_initialize_with_incorrect_parameter_should_raise_exception
    assert_raise(RuntimeError) { PostfixToInfix.new(1) }
    assert_raise(RuntimeError) { PostfixToInfix.new([]) }
    assert_raise(RuntimeError) { PostfixToInfix.new({}) }
  end
  
  def test_convert_sample_cases_verbose
    VALID_CASES.each do |sample|
      assert_nothing_raised(Exception) { ps2i = PostfixToInfix.new(sample[:postfix]) }
      ps2i = PostfixToInfix.new(sample[:postfix])
      assert_equal(sample[:infix_verbose], ps2i.convert)
    end
  end
end
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