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Why java Arrays use two different sort algorithms for different types?
So I was reading the Arrays doc on the various sort implementations. What I noticed was that some of the implementations used a tuned quicksort while others used a modified mergesort. Why the discrepancy?
Thanks!
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A simple solution would be to use efficient sorting algorithms like Merge Sort, Quicksort, Heapsort, etc., that can solve this problem in O(n. log(n)) time, but those will not take advantage of the fact that there are many duplicated values in the array. A better approach is to use a counting sort.
Additional storage space requirement : Merge sort is not in place because it requires additional memory space to store the auxiliary arrays. The quick sort is in place as it doesn't require any additional storage.
To use merge sort to remove duplicates, you would ignore elements that are repeated in the merging process.
3-way QuickSort performs very well when there are large number of duplicates. Save this answer.
Quicksort is used for arrays of primitive types while mergesort for Object[] arrays.
The main reason why mergesort is used for Objects that mergesort is stable - it does not reorder elements that are equal: http://en.wikipedia.org/wiki/Sorting_algorithm#Stability
For primitives the stability of the sort is meaningless, as you cannot distinguish two values that are equal. Hence, quicksort is used (except when sorting an array of Objects, for which mergesort is performed). Moreover, quicksort can be done in place, so there is no need to allocate another array.
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