(Previous discussion continued) | ||
Re: Wording of the rationale | Per Bothner | 08 Nov 2006 02:53 UTC |
Re: Wording of the rationale Per Bothner 08 Nov 2006 02:53 UTC
Jens Axel Søgaard wrote: > * Four varieties of algorithms were provided (quick, heap, > insert, merge) even though quick, heap, and insert sorts have > no significant advantage over merge-sort. > ... > Second: What does "no significant advantage" mean? I were of the > impression, that the "hidden constants" of O(n log (n)) of > vector-quick-sort were smaller than that of vector-merge-sort. My impression is that is non-trivially faster when you're sorting an array of integers, with no indirection through a "compare" function. In practice, one (almost) never sorts an array of integers (one sorts an array of records/objects - which may have integer fields), and one usually indirects though a compare function. That changes the "constant factors" significantly. It is illustrative that java.util.Arrays uses a "tuned quicksort" for sorting arrays of "primitive" (unboxed) numbers, but a "modified mergesort" to sort Object arrays. > Also: Is merge-sort the fastest algorithm, if the elements are "almost > sorted"? From the Java documentation: This [modified merge-sort] algorithm offers guaranteed n*log(n) performance, and can approach linear performance on nearly sorted lists. -- --Per Bothner xxxxxx@bothner.com http://per.bothner.com/