David Eppstein's WWW page http://www.ics.uci.edu/~eppstein/161/kmp/ contains an implementation of the Knuth-Morris-Pratt string matching algorithm in C++. It exists as a teaching example from his algorithms course notes.

He also provides a Mathematica code for the Minkowski sum problem in http://www.ics.uci.edu/~eppstein/junkyard/ukraine/ , which computes Minkowski sums of line segments (aka zonotopes). This problem is also closely related to maintaining line arrangements. The program works in any dimension, but doesn't do Minkowski sums of more complicated shapes.