#### Overview of this book

Choosing the right data structure is pivotal to optimizing the performance and scalability of applications. This new edition of Hands-On Data Structures and Algorithms with Python will expand your understanding of key structures, including stacks, queues, and lists, and also show you how to apply priority queues and heaps in applications. You’ll learn how to analyze and compare Python algorithms, and understand which algorithms should be used for a problem based on running time and computational complexity. You will also become confident organizing your code in a manageable, consistent, and scalable way, which will boost your productivity as a Python developer. By the end of this Python book, you’ll be able to manipulate the most important data structures and algorithms to more efficiently store, organize, and access data in your applications.
Preface
Free Chapter
Python Data Types and Structures
Introduction to Algorithm Design
Algorithm Design Techniques and Strategies
Stacks and Queues
Trees
Heaps and Priority Queues
Hash Tables
Graphs and Algorithms
Searching
Sorting
Selection Algorithms
String Matching Algorithms
Other Books You May Enjoy
Index

# Randomized selection

The randomized selection algorithm is used to obtain the `k`th smallest number that is based on the quicksort algorithm; the randomized selection algorithm is also known as quickselect. In Chapter 11, Sorting, we discussed the quicksort algorithm. The quicksort algorithm is an efficient algorithm to sort an unordered list of items. To summarize, the quicksort algorithm works as follows:

1. It selects a pivot.
2. It partitions the unsorted list around the pivot.
3. It recursively sorts the two halves of the partitioned list using steps 1 and 2.

One important fact about quicksort is that after every partitioning step, the index of the pivot does not change, even after the list becomes sorted. This means that after each iteration, the selected pivot value will be placed in its correct position in the list. This property of quicksort enables us to obtain the `k`th smallest number without sorting the complete list. Let’s discuss the randomized...