# File lib/text/levenshtein.rb, line 32
  def distance(str1, str2)
    prepare =
      if "ruby".respond_to?(:encoding)
        lambda { |str| str.encode(Encoding::UTF_8).unpack("U*") }
      else
        rule = $KCODE.match(/^U/i) ? "U*" : "C*"
        lambda { |str| str.unpack(rule) }
      end

    s, t = [str1, str2].map(&prepare)
    n = s.length
    m = t.length
    return m if n.zero?
    return n if m.zero?

    d = (0..m).to_a
    x = nil

    n.times do |i|
      e = i + 1
      m.times do |j|
        cost = (s[i] == t[j]) ? 0 : 1
        x = [
          d[j+1] + 1, # insertion
          e + 1,      # deletion
          d[j] + cost # substitution
        ].min
        d[j] = e
        e = x
      end
      d[m] = x
    end

    return x
  end