From: Robert Klemme Date: 2004-07-12T22:52:23+09:00 Subject: Re: A little algorithmic help requested... "Jason Creighton" schrieb im Newsbeitrag news:20040711153514.4b895d41.androflux@softhome.net.remove.to.reply... > On Sun, 11 Jul 2004 16:10:34 +0900, > Hal Fulton wrote: > > > Here's a problem my tired brain is having trouble with. > > > > Given a sorted array of integers, convert them into as many > > ranges as possible (ranges of three or more). > > > > Example: > > [1,2,3,4,6,7,8,11,12,15,16,17] ==> [1..4,6..8,11,12,15..17] > > > > How would *you* do this? > > Here's one that doesn't follow that "need at least three of more" > limitation, but it's how *I* would do it, because it returns an array of > *only* ranges, which seems like it would be more fun to deal with that a > mix of ranges and numbers. > > module Enumerable > def to_ranges > ranges = Array.new > self.sort.each do |e| > if ranges[-1] == nil or ranges[-1].end.succ != e > ranges << Range.new(e,e) > next > end > ranges[-1] = Range.new(ranges[-1].begin, e) > end > return ranges > end > end Nice and short, although I'd use "else" instead of "next"! :-) However, there is a performance drawback: you recreate ranges all over again. In the worst case of an array that contains all numbers from 1 to 1000 you create 999 Range instances and keep only one of them. That's not efficient. IMHO a solution in module Enumerable (i.e. a general solution) should do better with respect to time and space. Regards robert