How to calculate order (big O) for more complex algorithms (eg quicksort)

Question

I know there are quite a bunch of questions about big O notation, I have already checked:

• Plain english explanation of Big O
• Big O, how do you calculate/a

Answer 1

When applying a divide-and-conquer algorithm where you partition the problem into sub-problems until it is so simple that it is trivial, if the partitioning goes well, the size of each sub-problem is n/2 or thereabout. This is often the origin of the log(n) that crops up in big-O complexity: O(log(n)) is the number of recursive calls needed when partitioning goes well.