快速排序算法是基于分治策略的另一个排序算法。其基本思想是，对于输入的字数组a[p:r]，按以下3个步骤进行排序：

（1）分解：以a[p]为基准元素将a[p:r]划分成3段a[p:q-1],a[q]和a[q+1:r]，使得a[p:q-1]中任何元素小于等于a[q]，a[q+1:r]，中的任何元素大于等于a[q]。下标q在划分过程中确定

（2）递归求解：通过递归调用快速排序算法，分别对a[p:q-1]和a[q+1:r]进行排序

（3）合并：在a[p:q-1]和a[q+1:r]已经排好序的情况下，不需要执行任何运算，a[p:r]就已排好序

平均算法复杂度O(nlogn)-Quick sort algorithm is based on the sub-rule strategy to another sorting algorithm. The basic idea is that the word group for the importation of a [p: r], according to the following three steps to sort: (1) Decomposition: to a [p] as the base element would be a [p: r] is divided into 3 paragraphs a [p: q-1], a [q] and a [q+ 1: r], makes a [p: q-1] of any element less than or equal to a [q], a [q+ 1: r] , any element greater than or equal to a [q]. Subscr ipt q in the demarcation process to determine (2) Recursive Solution: recursive call through the quick sort algorithm, respectively, of a [p: q-1] and a [q+ 1: r] sort (3) the merger: the a [p: q-1] and a [q+ 1: r] has lined up sequence of circumstances, do not need to perform any computation, a [p: r] has lined up an average sequence algorithm complexity O (nlogn)