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quick sort

A sorting technique that sequences a list by continuously dividing the list into two parts and moving the lower items to one side and the higher items to the other. It starts by picking one item in the entire list to serve as a pivot point. The pivot could be the first item or a randomly chosen one. All items that compare lower than the pivot are moved to the left of the pivot; all equal or higher items are moved to the right. It then picks a pivot for the left side and moves those items to left and right of the pivot and continues the pivot picking and dividing until there is only one item left in the group. It then proceeds to the right side and performs the same operation again. See sort algorithm.

Quick Sorting a List
This quick sort uses randomly chosen pivots (in red) to keep dividing the list into two until there is only one item on each side of the pivot left.

sort algorithm

A formula used to reorder data into a new sequence. Like all complicated problems, there are many solutions that can achieve the same results, and one sort algorithm can re-sequence data faster than another. In the early 1960s, when magnetic tape was "the" storage medium, the sale of a computer system may have hinged on the sort algorithm, since without direct access capability on disk, every transaction had to be sorted into the sequence of the master files in order to update them. Today, sorting is not quite as conspicuous a process as it used to be; however, reports are still presented in sequential order, and myriad indexes to hard disk data must be maintained in a sequential order.

In-Memory Sorting
Today's considerably larger memories enable many sorts to be performed entirely in memory. However, if there is insufficient memory, a sort program may be able to store data that is partially sorted temporarily on disk and merge that data later into the final sequence. See bubble sort, insertion sort, merge sort, quick sort, selection sort, pigeonhole sort and counting sort.

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