snippet.rb

class String
  def - other
    @___m = Array.new(self.size) { [] }
    ___d(self, other)
  end
  
  private
  
  def ___d first, other
    n, m = first.size-1, other.size-1
    return [first.size, other.size].max if first.empty? || other.empty?
    # return 0 if self.empty? # Yeah?
    @___m[n][m] ||= if first[n] != other[m]
      1 + [
        # insert
        ___d(first[0..-2], other[0..-1]),
        # substitute
        ___d(first[0..-2], other[0..-2]),
        # delete
        ___d(first[0..-1], other[0..-2]),
      ].min
    else
      ___d(first[0..-2], other[0..-2])
    end
  end  
end

puts "WTF my Interwebz?" - "GTFO my Interwebz!"