Included recipe for matching two or more strings (i.e. calculating an edit distance).

Author: Allen Goodman

chapters/strings/matching-strings.md

@@ -0,0 +1,42 @@
+---
+layout:   recipe
+title:    Matching Strings
+chapter:  Strings
+---
+## Problem
+
+You want to match two or more strings.
+
+## Solution
+
+Calculate the edit distance, or number of operations required to transform one string into the other.
+
+{% highlight coffeescript %}
+Levenshtein =
+  (str1, str2) ->
+          
+    l1 = str1.length
+    l2 = str2.length
+    
+    Math.max l1, l2 if Math.min l1, l2 == 0      
+    
+    i = 0; j = 0; distance = []
+
+    for i in [0...l1 + 1]
+      distance[i] = []
+      distance[i][0] = i
+
+    distance[0][j] = j for j in [0...l2 + 1]
+    
+    for i in [1...l1 + 1]
+      for j in [1...l2 + 1]
+        distance[i][j] = Math.min distance[i - 1][j] + 1,
+          distance[i][j - 1] + 1,                         
+          distance[i - 1][j - 1] + if str1.charAt(i - 1) == str2.charAt(j - 1) then 0 else 1
+
+    distance[l1][l2]
+{% endhighlight %}
+
+## Discussion
+
+You can use either Hirschberg or Wagner–Fischer's algorithm to calculate a Levenshtein distance. This example uses Wagner–Fischer's algorithm.