This calculates the similarity between two strings as described in Programming Classics: Implementing the World's Best Algorithms by Oliver (ISBN 0-131-00413-1). Note that this implementation does not use a stack as in Oliver's pseudo code, but recursive calls which may or may not speed up the whole process. Note also that the complexity of this algorithm is O(N**3) where N is the length of the longest string.
The first string.
The second string.
Swapping the string1 and string2 may yield a different result; see the example below.
By passing a reference as third argument, similar_text will calculate the similarity in percent, by dividing the result of similar_text by the average of the lengths of the given strings times 100.
Returns the number of matching chars in both strings.
The number of matching characters is calculated by finding the longest first common substring, and then doing this for the prefixes and the suffixes, recursively. The lengths of all found common substrings are added.