From: Brian Candler <B.Candler@...>
Date: 2007-08-06T19:01:03+09:00
Subject: Re: Determining the common prefix for several strings

Here's a simple solution from my simple brain. It just takes the common
prefix between the first two items, then the common prefix between this and
the third, etc.

arr = %w{
item001
item004
item002
item002b
item002C
item_5
item_10
itemize_this
}

prefix = arr.first.dup
arr[1..-1].each do |e|
  prefix.slice!(e.size..-1) if e.size < prefix.size   # optimisation
  prefix.chop! while e.index(prefix) != 0
end
puts prefix