From: Raj Sahae <rajsahae@...>
Date: 2007-04-09T17:32:50+09:00
Subject: Re: [QUIZ] Getting to 100 (#119)

Christian Neukirchen wrote:
> =begin
>   
>> The quiz, then, is to solve this problem without thinking, instead
>> letting the computer think for you.
>>     
>
> I did not intent to seriously submit this solution, but it can be
> helpful as an example of how to use Ruby to solve a problem quickly
> without thinking too much or locating Knuth on the bookshelve.
> Writing this code took maybe ten minutes and happened step-by-step
> with checking the immediate results.
>
> Since there are only 168 solutions (254 if you allow a sign before the
> first digit), brute-forcing is the simplest thing one can do.
> Additional operations can be added by changing the base and mapping
> the digits onto further operations.  (Different digit order is not
> that easy to implement and maybe be futile to do with brute-forcing.)
> =end
>
> (00000000..'22222222'.to_i(3)).map { |x| x.to_s(3).rjust(8, "0").
>                                                    tr('012', '-+ ') }.
>   find_all { |x| x.count("-") == 2 and x.count("+") == 1 }.
>   map { |x|
>     t = "1" + x.split(//).zip((2..9).to_a).join.delete(" ")
>     [eval(t), t]
>   }.sort.each { |s, x|
>     puts "*****************" if s == 100
>     puts "#{x}: #{s}"
>     puts "*****************" if s == 100
>   }
>
> __END__
>
> 2#787<p4>lilith:~/mess/current$ ruby quiz119.rb |grep -C4 100$
> 123-456-7+89: -251
> 123+45-67-89: 12
> 123-45+67-89: 56
> *****************
> 123-45-67+89: 100
> *****************
> 12+345-67-89: 201
> 1-234+567-89: 245
> 1-23-456+789: 311
>
>   
I'm sorry to be a noob on this, but can someone please explain to me 
what this is doing.  If it works, it must be genius, and I can't figure 
it out.

Raj Sahae