Is there an easy way to work out the Big O value for time and space complexity?

Question

I have been learning about sorting algorithms and understand the idea of time and space complexity. I was wondering if there was a fairly quick and easy way of working out the complexities given the algorithm (one that may even be quick enough to do in an exam) as opposed to learning all of the complexities for the algorithms.

If this isn't an option, is there an easy way to remember or learn them for some of the more basic sortings algorithms such as merge sort and quicksort.

Answer 1

You have to memorize this:

It depends on the problem. Best option in different situations:

• In place and stable: Selection Sort
• In place (don't care about stable): Heap Sort
• Stable (don't care about in place): Merge Sort