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Quicksort: Python
Recurse, Rinse, Repeat

We’ve made it through the trickiest portion of the algorithm, but we’re not quite finished. We’ve partitioned the list once, but we need to continue partitioning until the base case is met.

Let’s revisit our example from the previous exercise where we had finished a single partition step:

# the pivot, 3, is correctly placed whole_list = [2, 1, (3), 4, 6, 5] less_than_pointer = 2 start = 0 end = len(whole_list) - 1 # start and end are pointers encompassing the entire list # pointers for the "lesser than" sub-list left_sub_list_start = start left_sub_list_end = less_than_pointer - 1 lesser_than_sub_list = whole_list[left_sub_list_start : left_sub_list_end] # [2, 1] # pointers for the "greater than" sub-list right_sub_list_start = less_than_pointer + 1 right_sub_list_end = end greater_than_sub_list = whole_list[right_sub_list_start : right_sub_list_end] # [4, 6, 5]

The key insight is that we’ll recursively call quicksort and pass along these updated pointers to mark the various sub-lists. Make sure you’re excluding the index that stores the newly placed pivot value or we’ll never hit the base case!

Instructions

1.

Complete our quicksort algorithm by recursively calling quicksort on the left and right sub-lists.

2.

Call quicksort() on unsorted_list. Be sure to pass in all three arguments!

Print unsorted_list.

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