Definition: Pick an element from the array (the pivot), partition the remaining elements into those greater than and less than this pivot, and recursively sort the partitions. There are many variants of the basic scheme above: to select the pivot, to partition the array, to stop the recursion on small partitions, etc.
Generalization (I am a kind of ...)
Specialization (... is a kind of me.)
balanced quicksort, multikey Quicksort, introspective sort.
Aggregate child (... is a part of or used in me.)
partition, divide and conquer, recursion, Select, sublinear time algorithm.
See also external quicksort.
Note: Quicksort has running time Θ(n²) in the worst case, but it is typically O(n log n). In practical situations, a finely tuned implementation of quicksort beats most sort algorithms, including sort algorithms whose theoretical complexity is O(n log n) in the worst case.
Select can be used to always pick good pivots, thus giving a variant with O(n log n) worst-case running time.
Java applet animation (Java). Comparison of quicksort, heapsort, and merge sort on modern processors.
If you have suggestions, corrections, or comments, please get in touch with Paul E. Black.
Entry modified 24 August 2009.
HTML page formatted Tue Dec 6 16:16:32 2011.
Cite this as:
Conrado Martinez, "quicksort", in Dictionary of Algorithms and Data Structures [online], Paul E. Black, ed., U.S. National Institute of Standards and Technology. 24 August 2009. (accessed TODAY) Available from: http://www.nist.gov/dads/HTML/quicksort.html