From: Jeff de Vries <jdevries@...>
Date: 2006-04-30T07:35:10+09:00
Subject: Re: Learn to Program, by Chris Pine

Restricting to what is covered in chapters 1-10, how about the  
following?

def sort some_array
   recursive_sort some_array, []
end

def recursive_sort unsorted_array, sorted_array
   if unsorted_array.size == 0
     return sorted_array
   else
     smallest = unsorted_array[0]
     unsorted_array.each do |x|
       if x < smallest
         smallest = x
       end
     end
     new_unsorted_array = []
     unsorted_array.each do |x|
       if x == smallest
         sorted_array.push(x)
       else
         new_unsorted_array.push(x)
       end
     end
     recursive_sort new_unsorted_array, sorted_array
   end
end

On Apr 29, 2006, at 11:38 AM, Colin wrote:

>
> Hello,
>
> thank you very much for all these good answers
> (especially to Jan_K and Dave Burt ).
>
> Im learning ruby with the same book and get stuck
> in chapter 10.2 Rite of Passage:Sorting
> this exercise is about array sort algorithms.
> Instead of 'array.sort' i have to program my own sort method.
>
> chris pine gives a few hints:
> using < to find the smallest word in a list
>
> take two lists  in the method
>
> and these two empty methods
>
> def sort some_array
>   recursive_sort some_array, []
>
> end
>
> def recursive_sort unsorted_array, sorted_array
>
> end
>
>
> After a lot of trying and searching ...
>
> ...I found the quicksort algorithm and this code
>
> def quicksort( array )
>     if array.size <= 1
>         array
>     else
>         ls, rest = array.partition { |i| i < array[0] }
> 	puts 'ls:'+ls.to_s
> 	puts 'rest:'+rest.to_s
>         rs, rest = rest.partition { |i| i > array[0] }
> 	puts 'rs:'+rs.to_s
> 	puts 'rest2:'+rest.to_s
>         quicksort( ls ) + rest + quicksort( rs )
>
>
>     end
> end
>
> Yes this is a possible solution, but array.partion ,double
> assignments(ls,rest)
> of variables,arrays and the 'short block' (like { |i| i > array[0] })
> are not mentioned in any chapter before.
>
> Although I understand the Code above , I'm looking for an easy  
> solution
> that don't leave the scope of chaper 1 to 10 .
>
> Here's my own code, but it doesn't work .
>
>
> def ownsort unsort, sort
>  rest=[]
>  rs=[]
>  if unsort.size <= 1
>    unsort
>  else
>    unsort.each do |i|
>      if i <unsort[0]
>
>        sort.push i
>      else
>        rest.push i
>      end
>    end
>
>  end
>   rest
> end
>
>
> thanks for reading and hopefully some hints...
>
> colin
>
>
> -- 
> Posted via http://www.ruby-forum.com/.
>