Quicksort slower than Mergesort?

Question

I was working on implementing a quicksort yesterday, and then I ran it, expecting a faster runtime than the Mergesort (which I had also implemented). I ran the two, and while th

Answer 1

One of the advantages of quicksort for relatively small array sizes is just an artifact of hardware implementation.

On arrays, quicksort can be done in-place, meaning that you're reading from and writing to the same area of memory. Mergesort, on the other hand, typically requires allocating new buffers, meaning your memory access is more spread out. You can see both of these behaviors in your example implementations.

As a result, for relatively small datasets, quicksort is more likely to get cache hits and therefore just tends to run faster on most hardware.

Mergesort is still a pretty good solution for large data sets or other data structures, like linked lists, as your experiments confirm.