1 files changed, 44 insertions, 0 deletions
diff --git a/guides/rails_guides/levenshtein.rb b/guides/rails_guides/levenshtein.rb
new file mode 100644
index 0000000000..2213ef754d
--- /dev/null
+++ b/guides/rails_guides/levenshtein.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module RailsGuides
+  module Levenshtein
+    # This code is based directly on the Text gem implementation.
+    # Copyright (c) 2006-2013 Paul Battley, Michael Neumann, Tim Fletcher.
+    #
+    # Returns a value representing the "cost" of transforming str1 into str2
+    def self.distance(str1, str2)
+      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
+  end
+end