From: Daniel Lucraft <dan@...>
Date: 2007-07-19T18:14:33+09:00
Subject: Re: confused, need help with a sorting program

johny.lam wrote:
> I was doing the recursive sorting program in Chapter 10 of Chris
> Pine's learning to program and i wrote this:
> 
> what i don't get is that this program sorts the words into reverse
> alphabetical order.

> what i am trying to is move the smallest word into the sorted_array
> but if i use the greater than sign wouldn't the move the biggest word
> into the sorted_array?

Yes, that's true. The problem here is that you are not calling the 
function recursively with sorted_array. The sorted_array is getting 
discarded at each level and replaced with [] each time, since you're 
calling 'sort' instead of 'recursive_sort'.

There is a little illusion here, which you will see if you change the 
'puts' to a 'p'. You are not actually getting an full array out the end, 
it just looks like you are because you are printing the elements one at 
a time.

You need to pass the sorted_array down into the next level of 
recursive_sort, by
changing

  unsorted_array.pop
  sort(unsorted_array)

to

  unsorted_array.pop
  recursive_sort(unsorted_array, sorted_array)

Now this will print out the sorted array n times, since as each 
recursive_sort returns, it will look at the now empty unsorted_array and 
then print sorted_array. I'd get rid of

  if unsorted_array.length==0
    p sorted_array   # <-- was 'puts'
  end

altogether and arrange it so that the sort function returns the sorted 
array:

  def recursive_sort unsorted_array, sorted_array
    ...
    return sorted_array
  end

  ...

  # call the sort function
  p sort(word)



best,
Dan

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