## The Mastery of Computer Programming: Primary Algorithms - Sykalo Eugene 2023

# Internal sorting

Sorting and Searching

## Introduction to internal sorting

Internal sorting is the process of sorting data within the main memory of a computer. This is in contrast to external sorting, which involves sorting data that is too large to fit into memory and must be stored on disk. Internal sorting is important because it is often much faster than external sorting due to the faster access times of main memory.

There are many different algorithms that can be used for internal sorting, and the choice of algorithm can have a significant impact on the sorting performance. Some of the most common sorting algorithms include bubble sort, selection sort, insertion sort, quicksort, and mergesort. Each algorithm has its own strengths and weaknesses, and the choice of algorithm will depend on the specific requirements of the application.

In addition to the choice of algorithm, the performance of internal sorting can also be affected by the data being sorted. For example, sorting data that is already partially sorted can be much faster than sorting completely unsorted data. Sorting data that has a lot of duplicates can also be faster, as some algorithms can take advantage of duplicate values to speed up the sorting process.

## Comparison-based sorting algorithms

Comparison-based sorting algorithms are a class of algorithms that rely on comparing pairs of elements in the input sequence. The most common comparison-based sorting algorithms include bubble sort, selection sort, and insertion sort.

### Bubble sort

Bubble sort is a simple sorting algorithm that works by repeatedly swapping adjacent elements if they are in the wrong order. The algorithm continues iterating through the list until no more swaps are needed. Bubble sort has a worst-case time complexity of O(n^2), making it inefficient for large input sizes.

### Selection sort

Selection sort works by repeatedly finding the minimum element from the unsorted part of the list and moving it to the front of the sorted part of the list. The algorithm continues until the entire list is sorted. Selection sort has a worst-case time complexity of O(n^2), making it inefficient for large input sizes.

### Insertion sort

Insertion sort works by iteratively inserting each element of the list into its proper position in a sorted sublist. The algorithm starts with an empty sorted sublist and inserts each element in order, one at a time. Insertion sort has a worst-case time complexity of O(n^2), making it inefficient for large input sizes.

While comparison-based sorting algorithms are conceptually simple and easy to implement, they can be inefficient for large input sizes. As a result, non-comparison-based sorting algorithms are often used for large-scale sorting tasks.

## Non-comparison-based sorting algorithms

Non-comparison-based sorting algorithms are a class of algorithms that do not rely on comparing pairs of elements in the input sequence. Instead, they use other properties of the data to sort it. These algorithms can be much faster than comparison-based sorting algorithms, especially for large input sizes.

### Radix sort

Radix sort is a non-comparison-based sorting algorithm that works by sorting the input data one digit at a time. The algorithm first sorts the data based on the least significant digit, then the next least significant digit, and so on, until the data is sorted by all digits. Radix sort has a worst-case time complexity of O(kn), where k is the number of digits in the largest number, making it very efficient for large input sizes.

### Bucket sort

Bucket sort is a non-comparison-based sorting algorithm that works by dividing the input data into a set of buckets and then sorting each bucket individually. The algorithm first determines the range of values in the input data and then creates a bucket for each range of values. The input data is then distributed into the appropriate bucket, and each bucket is sorted individually using another sorting algorithm. Bucket sort has a worst-case time complexity of O(n^2), but in practice, it can be much faster than comparison-based sorting algorithms for certain types of data.

Non-comparison-based sorting algorithms can be highly efficient for large input sizes, but they can also be more complex to implement than comparison-based sorting algorithms. The choice of algorithm will depend on the specific requirements of the application and the characteristics of the data being sorted.

## Analysis of sorting algorithms

The performance of a sorting algorithm can be measured in terms of time complexity and space complexity. Time complexity refers to the amount of time it takes for the algorithm to complete as a function of the input size, while space complexity refers to the amount of memory required by the algorithm as a function of the input size.

### Time complexity

The time complexity of a sorting algorithm can be expressed using Big O notation, which provides an upper bound on the growth rate of the algorithm's running time. The time complexity of a sorting algorithm depends on the algorithm's basic operations, such as comparisons and swaps, as well as the input size and the characteristics of the data being sorted.

Some of the most common time complexities for sorting algorithms include:

- O(n^2): This is the worst-case time complexity for many comparison-based sorting algorithms, such as bubble sort, selection sort, and insertion sort. These algorithms are inefficient for large input sizes, but they are simple to implement and can be useful for small input sizes.
- O(n log n): This is the time complexity of many efficient comparison-based sorting algorithms, such as quicksort and mergesort. These algorithms are much faster than O(n^2) algorithms for large input sizes, but they can be more complex to implement.
- O(n): This is the time complexity of some non-comparison-based sorting algorithms, such as radix sort and bucket sort. These algorithms can be highly efficient for certain types of data, but they may require more memory than comparison-based sorting algorithms.

### Space complexity

The space complexity of a sorting algorithm refers to the amount of memory required by the algorithm as a function of the input size. For internal sorting, the space complexity is usually measured in terms of the additional memory required by the algorithm, beyond the memory used to store the input data.

Many sorting algorithms have a space complexity of O(1), meaning that they require a constant amount of additional memory regardless of the input size. However, some algorithms, such as mergesort, have a space complexity of O(n), meaning that they require additional memory proportional to the input size.

## Implementing sorting algorithms

Implementing sorting algorithms can be straightforward, but it requires attention to detail to ensure that the algorithm is working correctly and efficiently. Here are some general steps to follow when implementing a sorting algorithm:

- Choose an appropriate programming language and environment for the algorithm. Some languages, such as Python, have built-in sorting functions that can be used instead of implementing a sorting algorithm from scratch.
- Develop a clear understanding of the algorithm you want to implement, including its time and space complexity, basic operations, and any specific requirements for the algorithm.
- Choose appropriate data structures to use for the algorithm. For example, an array may be a good choice for some algorithms, while a linked list may be better for others.
- Write the algorithm code, making sure to follow best practices for coding, such as using meaningful variable names and commenting the code.
- Test the algorithm thoroughly, using a variety of inputs, including edge cases and large input sizes. Test the algorithm's performance, including its time and space complexity, and compare it to other sorting algorithms if possible.
- Optimize the algorithm if necessary, by finding ways to reduce its time or space complexity or improve its performance in other ways.
- Document the algorithm thoroughly, including its purpose, inputs, outputs, and any limitations or known issues.

When implementing a sorting algorithm, it can be helpful to use a template or framework to guide the process. For example, some programming languages provide built-in functions or libraries for sorting that can be used as a starting point. There are also many open-source sorting algorithms available online that can be used as a reference or starting point for custom implementations.