Knuth-Morris-Pratt - Pattern Matching 

I agree this is likely the best one. Hopefully it's not too hard for struggling students to find because it should clear things right up.

Cause two characters are matching....so the prefix and suffix is 'ab'

It's O(n). I find this video a better explanation of KMP since it goes over more examples and how to calculation the failure function in depth. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-GTJr8OvyEVQ.html

Right, it should be "j = j + 1" and not "j + j + 1". I think that the mistake is small enough and obvious enough that the people will understand. Thanks for helping.