Quick Sort

This is used in research code when built-in qsort does not satisfy the demands.

K-th element

Qsort can be used to find the Kth smallest element a[k]:

In Python,


Use partition to sort 0, 0, 0, 1, 1, 2, 2, 2…


Merge Sort

Linked List Version

Here is the merge sort when qsort does not work:

Array Version



Given two sorted arrays A and B, merge B into A:

What about Lists?

Bucket Sort


Find the first missing positive


Bubble Sort


Sort 4 Elements