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From: Harry Kakueki <list.p...@gmail.com>
Newsgroups: comp.lang.ruby
Subject: Re: [QUIZ] Postfix to Infix (#148)
Date: Sun, 2 Dec 2007 10:09:23 -0500
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>
> This week's quiz is to write a script that translates postfix expressions into
> the equivalent infix expression.  In the simplest form, your script should
> function as such:
>
>         $ ruby postfix_to_infix.rb '2 3 +'
>         2 + 3
>
> At minimum, try to support the four basic math operators:  +, -, *, and /.  Feel
> free to add others though.  For numbers, remember to accept decimal values.
>
# Here is my solution.
# It solves the minimum requirements with minimal error checking.
# Removes some parentheses.
#str = "1 56 35 + 16 9 - / +"
str = "1 2 - 3 4 - - 2 * 7.4 + 3.14 * 2 / 1.2 + 3 4 - -"
ops = %w[+ - * /]
arr = str.split(/\s+/)
err = arr.select {|c| c =~ /^\d+\.?\d?/ || ops.include?(c)}
the_stack = []

if arr.length == err.length
  arr.each_with_index do |x,y|
  the_stack << x unless ops.include?(x)
    if ops.include?(x) && the_stack.length > 1
    b = the_stack.pop
    a = the_stack.pop
    the_stack << "(#{a} #{x} #{b})" if (x == "+" || x == "-") && (y <
(arr.length - 1))
    the_stack << "#{a} #{x} #{b}" if x == "*" || x == "/" || y ==
(arr.length - 1)
    end
  end
  puts the_stack[0]
end

# Harry


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