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

I ran similar tests and pure quick sort (with random choice of pivot) turned out to be much slower than merge sort for large arrays.

Choosing the pivot as the median of the first, middle and last element improved quick sort`s performance, but quick sort was still definitely worse than merge sort on large arrays (> 100000 elements).

I saw a big improvement when I implemented intro-sort, i.e. quick sort that falls back to heap sort if the recursion depth exceeds a certain threshold. My intro-sort implementation was almost as fast as my merge sort implementation. Of course, intro-sort is no longer pure quick sort as it uses heap sort to bring the complexity back to n log(n) when pure quick sort hits some bad data. I can post the results if you are interested.