Gem::Text#levenshtein_distance

# File tmp/rubies/ruby-3.1.3/lib/rubygems/text.rb, line 55
def levenshtein_distance(str1, str2)
  n = str1.length
  m = str2.length
  return m if n.zero?
  return n if m.zero?

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

  # to avoid duplicating an enumerable object, create it outside of the loop
  str2_codepoints = str2.codepoints

  str1.each_codepoint.with_index(1) do |char1, i|
    j = 0
    while j < m
      cost = (char1 == str2_codepoints[j]) ? 0 : 1
      x = min3(
        d[j + 1] + 1, # insertion
        i + 1,      # deletion
        d[j] + cost # substitution
      )
      d[j] = i
      i = x

      j += 1
    end
    d[m] = x
  end

  x
end