Problem
1. Write a function that sorts a linked list.
2. Write an industrial-strength quicksort function with the following enhancements:
a. If an array segment contains 20 elements or fewer, sort it using insertion sort.
b. After sorting the first, middle, and last elements, use the median as the pivot, instead of swapping the median with the first element. (Save this value in pivot_val). Because the first and last elements are in the correct partitions, it is not necessary to test them before advancing up and down. This is also the case after each exchange, so increment up and decrement down at the beginning of the do . . . while loop. Also, it is not necessary to test whether up is less than last before incrementing up, because the condition pivot_val < *up is false when up equals last - 1 (the median must be ≥ the last element in the>