From: Mathieu Bouchard <matju@...>
Date: 2001-03-10T03:08:24+09:00
Subject: [ruby-talk:12344] Re: ...and the challenge

> On Sat, 10 Mar 2001, Robert Feldt wrote:
> > Hi again,
> > Yes I forgot the challenge:
> > Write a nice, fast and small Ruby program for generating the n
> > first numbers in the Hamming sequence defined as
> > "List of all numbers, in ascending order, of the form
> > (2**i)*(3**j)*(5**k) for i,j,k at least 0. It begins like
> > 	1 2 3 4 5 6 8 9 10 12 15 16 18 ..."
> Here's one for a start. it's not fast though.
> 	def suck(i,x); while x%i==0; x/=i; end; x; end
> 	n=1; loop do p n if 1 == (suck 2, suck 3, suck 5, n); n+=1; end

limiting it to 1_000_000, it takes 27 seconds to run.

I then tried this one:


	n=1_000_000
	nums=[]
	(0..20).each{|a|
		(0..13).each{|b|
			(0..9).each{|c|
				x = 2**a * 3**b * 5**c
				nums << x if x <= n
			}
		}
	}
	nums.sort!
	nums.each{|x|p x}


This takes 0.35 second here.

matju