Second stab at shortening a sting. Is this brute enough?

shorten2.rb

$cache = {} 

def shorten(s, ws)
  $cache[s] ||= ws.flat_map { |w| 
    a = s.split(w, -1)
    (0..a.size-1).map { |p|
      ns = a[0..p].join(w) + a[p+1..-1].join(w)
      ns.size < s.size ? shorten(ns, ws) : s
    }
  }.min_by { |s| s.size }
end