From: Colin <c.esch@...>
Date: 2006-04-30T03:38:55+09:00
Subject: Re: Learn to Program, by Chris Pine


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


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