Introduction to three way quicksort

Three-way quicksort is an enhanced version of the traditional quicksort algorithm, designed specifically to handle datasets containing many duplicate values.

In the classic quicksort algorithm, the list is partitioned into two parts: one with elements less than the pivot (the chosen reference element) and the other with elements greater than the pivot. However, if the list contains many duplicates, this approach can be inefficient because it may lead to unbalanced partitions. Three-way quicksort addresses this issue by partitioning the list into three parts:

• Elements less than the pivot
• Elements equal to the pivot
• Elements greater than the pivot

It only applies the algorithm to the first and last parts, ignoring the middle part (the elements equal to the pivot are already in their correct sorted positions). This allows the algorithm to handle lists with many duplicate elements more efficiently.

Example