The PrefixDistance(s,t) and SuffixDistance(s,t) commands return integer measures of the distance between the two strings s and t.

Let s and t be arbitrary strings. The prefix distance PrefixDistance( s, t ) is defined to be $\mathrm{length}\left(s\right)+\mathrm{length}\left(t\right)-2\mathrm{CommonPrefix}\left(s\,t\right)$, and the suffix distance $\mathrm{SuffixDistance}\left(s\,t\right)$ is defined, similarly, to be $\mathrm{length}\left(s\right)+\mathrm{length}\left(t\right)-2\mathrm{CommonSuffix}\left(s\,t\right)$. Both are metrics.

Other string metrics available in this package include StringTools[HammingDistance] and StringTools[Levenshtein].

All of the StringTools package commands treat strings as (null-terminated) sequences of $8$-bit (ASCII) characters.  Thus, there is no support for multibyte character encodings, such as unicode encodings.

$\mathbf{use}\mathrm{StringTools}\mathbf{in}\mathrm{PrefixDistance}\left(''Mathematics''\,''Mathematische''\right)\mathbf{end\; use}$

$6$

$\mathrm{with}\left(\mathrm{StringTools}\right)\:$

$\mathrm{PrefixDistance}\left(''abc''\,''abd''\right)$

$2$

$\mathrm{PrefixDistance}\left(''abc''\,''abcd''\right)$

$1$

$\mathrm{PrefixDistance}\left(''Elisabeth''\,''Elyse''\right)$

$10$

$\mathrm{PrefixDistance}\left(''Connor''\,''Constance''\right)$

$9$

$\mathrm{SuffixDistance}\left(''foe''\,''Defoe''\right)$

$2$

$\mathrm{SuffixDistance}\left(''North\; America''\,''Central\; America''\right)$

$12$

$\mathrm{SuffixDistance}\left(''North\; America''\,''South\; America''\right)$

$6$

$\mathrm{SuffixDistance}\left(''abba''\,''abba''\right)$

$0$

$s≔\mathrm{Random}\left(10\,'\mathrm{binary}'\right)$

$s≔''0000101110''$

$t≔\mathrm{Random}\left(10\,'\mathrm{binary}'\right)$

$t≔''1101110100''$

$u≔\mathrm{Random}\left(10\,'\mathrm{binary}'\right)$

$u≔''0100010001''$

$\mathrm{SuffixDistance}\left(s\,t\right)$

$18$

$\mathrm{SuffixDistance}\left(s\,u\right)+\mathrm{SuffixDistance}\left(u\,t\right)$

$40$