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The main disadvantage of merge sort is that it is an out-of-place algorithm, so when operating on arrays, efficient implementations require O(n) auxiliary space (vs. O(log n) for quicksort with in-place partitioning and tail recursion, or O(1) for heapsort).
Consequently, quicksort needs O(log 2 n) additional space. Although this non-constant space technically takes quicksort out of the in-place category, quicksort and other algorithms needing only O(log n) additional pointers are usually considered in-place algorithms.
Efficient implementations of quicksort (with in-place partitioning) are typically unstable sorts and somewhat complex but are among the fastest sorting algorithms in practice. Together with its modest O(log n) space usage, quicksort is one of the most popular sorting algorithms and is available in many standard programming libraries.
Yes, my comment was meant to emphasize that most in-place partitioning algorithms are unstable, and most stable ones are not in place. Most variants of quicksort, however, are not in-place because they use a stack of depth at least log n (in fact, if the values being sorted may be arbitrarily large, it requires log 2 n space, where n is the ...
External sorting algorithms generally fall into two types, distribution sorting, which resembles quicksort, and external merge sort, which resembles merge sort. External merge sort typically uses a hybrid sort-merge strategy. In the sorting phase, chunks of data small enough to fit in main memory are read, sorted, and written out to a temporary ...
Quickselect uses the same overall approach as quicksort, choosing one element as a pivot and partitioning the data in two based on the pivot, accordingly as less than or greater than the pivot. However, instead of recursing into both sides, as in quicksort, quickselect only recurses into one side – the side with the element it is searching for.
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After all, QuickSort seems to be easily done in-place as shown in the Quicksort article. Quote: Although somewhat slower in practice on most machines than a good implementation of quicksort, it has the advantages of worst-case O(n log n) runtime and being an in-place algorithm. Quicksort is not in place, as the article discusses at some length.