One day I was searching for some kind of online calculator that will help me to calculate prefix function.
Unfortunately, I haven't found such. So that situation forced me to make my own :)
And if I made one, why not share it with people.
By the way, under the main part of the 'calculator' you can find the 'Learn more' section.
It either describes my approach to a certain problem or gives references to resources where you can figure out how to solve it