a-beginners-guide-to-big-o-notation

https://rob-bell.net/2009/06/a-beginners-guide-to-big-o-notation/

https://www.cs.utexas.edu/users/djimenez/utsa/cs1723/lecture2.html

https://www.interviewcake.com/article/big-o-notation-time-and-space-complexity

http://ftp.csd.uwo.ca/courses/CS1037a/notes/topic13_AnalysisOfAlgs.pdf