Question

I wanna implement a fast algorithm for a homework, but using parallel processing for this task. I heard that the parallel version of Quicksort is the best choice, but I’m not sure of this… maybe Heapsort is a good idea. Which algorithm do you think is the best one for a parallelized environment, and why?

Answer 1

Quick sort can split the unsorted list into two halves, but unfortunately, the halves aren’t guaranteed to be anywhere near even. So one machine (or half of a cluster of machines) could get 20 entries, and the other half could get 20 billion.

I can’t think of a good way to make heapsort work in parallel. It can be done, but man, that feels really counterintuitive.

Merge sort is the one I think you want.

• Each split is exactly 50% of the list, so it’s easy to split between processors.
• You can implement merge sort on two sets of tape drives, which means that it doesn’t require the whole list be in memory at one time. For large lists, especially those that are larger than the memory you have available, that’s a must have.
• Merge sort is also stable in parallel implementations, if it matters.