https://developerinsider.co/big-o-notation-explained-with-examples/

http://www.souravsengupta.com/cds2016/lectures/Complexity_Cheatsheet.pdf

https://medium.com/@salmaeng71/big-o-notation-cheat-sheet-4a7e5632c93e

Some interesting articles trying to explain Big-O notation.

Insultingly enough video is Tom Scott on his series called “The Basics”. It’s a nice introduction to it if you don’t know Big-O notation, A-Level students need to be able to identify what complexity a given algorithm is, and order the different types from best to worst.