From: William James <w_a_x_man@...>
Date: 2005-12-13T15:47:38+09:00
Subject: Re: A question about recursive programming

Hank Gong wrote:
> I want to calculate all sum possibility of interger array. I know there are
> other non-recursive way to do it.
> But when I wrote recursive code to achieve it, I just got error.
>
>
> def all_sum(arr)
>     b=arr if arr.length==1
>     temp=arr.delete_at(arr.length-1)
>     b=all_sum(arr)+all_sum(arr).collect{|i| i+temp}
> end
>
> c=[1,2]
> p all_sum(c)
>
> Error: in `all_sum': stack level too deep (SystemStackError)
>
> Can anyone give me some advice?


class Array
  def add( n )
    self.map{|item| item + n }
  end
  def tail
    self[1..-1]
  end
end

def sums( array )
  return []   if array.size < 2
  array.tail.add( array.first ) + sums( array.tail )
end