对顺序表的快速排序算法中，如何选取一个界值（又称为轴元素），影响着快速排序的效率，而且界值也并不一定是被顺序表中的一个元素。例如，我们可以用被划分序列中所有元素的平均值作为界值。编写算法实现以平均值为界值的快速排序方法。-On the the sequence table fast sorting algorithm, how to select a critical value (also known as the axis elements) affect the efficiency of the quick sort, and the critical value is not necessarily an element in the sequence table. For example, we can use the average of all of the elements in the sequence is divided as a boundary value. Write algorithms to achieve the quicksort method to the average for the sector.