levenshtein_distance

# File railties/lib/rails/command/spellchecker.rb, line 20
          def levenshtein_distance(str1, str2) # :doc:
            s = str1
            t = str2
            n = s.length
            m = t.length

            return m if 0 == n
            return n if 0 == m

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

            # avoid duplicating an enumerable object in the loop
            str2_codepoint_enumerable = str2.each_codepoint

            str1.each_codepoint.with_index do |char1, i|
              e = i + 1

              str2_codepoint_enumerable.with_index do |char2, j|
                cost = (char1 == char2) ? 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

            x
          end