From: Siep Korteling <s.korteling@...>
Date: 2008-11-07T05:51:00+09:00
Subject: Re: Finding gaps in a sorted sequence

Pete Hodgson wrote:
> Hi Folks,
> 
> Given a sorted enumeration I need to find the first gap in a sequence.
> 
> e.g.
> 3 == find_gap [1,2,4,5]
> nil == find_gap [1,2,3,4]
> 
> Here's the best I can come up with
> 
> def first_gap( seq )
>   seq.each_cons(2) do |l,r|
>     _next = l.next
>     return _next if r!= _next
>   end
>   nil
> end
> 
> but it seems rather ugly. Anyone have a more elegant implementation?
> 
> Cheers,
> Pete

The following does not quite meet your specs (it returns an array with 
all gaps, empty if there are no gaps). Anyway, here is my try:

def find_gaps( ar )
  (ar.first .. ar.last).to_a - ar
end

p find_gaps( [1,2,4,5] )
p find_gaps( ["a", "b", "d", "e", "h"] )

require 'date'
d1 = Date.new(2008,11,6)
d2 = Date.new(2008,11,7)
d3 = Date.new(2008,11,9)
puts find_gaps( [d1,d2,d3] )

=> [3]
=> ["c", "f", "g"]
=> 2008-11-08

hth,

Siep


-- 
Posted via http://www.ruby-forum.com/.