1 files changed, 39 insertions, 0 deletions
diff --git a/guides/rails_guides/levenshtein.rb b/guides/rails_guides/levenshtein.rb
new file mode 100644
index 0000000000..8a908a4339
--- /dev/null
+++ b/guides/rails_guides/levenshtein.rb
@@ -0,0 +1,39 @@
+module RailsGuides
+  module Levenshtein
+    # This code is based directly on the Text gem implementation
+    # 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
+      max = n/2
+
+      return m if (0 == n)
+      return n if (0 == m)
+      return n if (n - m).abs > max
+
+      d = (0..m).to_a
+      x = nil
+
+      str1.each_char.each_with_index do |char1,i|
+        e = i+1
+
+        str2.each_char.each_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
+
+      return x
+    end
+  end
+end