What is a quick sort in C and how is it implemented?

Table of Contents

• Introduction
• Key Components of Quick Sort
  • 1. Pivot Selection:
  • 2. Partitioning:
  • 3. Recursive Sorting:
  • 4. In-place Sorting:
• Implementing Quick Sort in C
  • Step 1: Partitioning the Array
  • Step 2: Quick Sort Recursion
  • Quick Sort Code in C
  • Code Breakdown:
  • Sample Output:
• Practical Example: Sorting a List of Test Scores
• Conclusion

Introduction

Quick sort is a popular and efficient sorting algorithm that follows the divide-and-conquer paradigm. It works by selecting a pivot element from the array, partitioning the array around the pivot so that elements smaller than the pivot come before it, and elements larger come after. This partitioning step is followed recursively on the left and right sub-arrays. Quick sort is preferred due to its average-case time complexity of O(n log n) and its ability to sort in-place, requiring minimal extra memory.

This guide walks through the quick sort algorithm and its implementation in C.

Key Components of Quick Sort

1. Pivot Selection:

A pivot element is chosen from the array to divide the elements into smaller and larger values.

2. Partitioning:

The array is reorganized so that all values smaller than the pivot are placed before it, and all larger values are placed after it.

3. Recursive Sorting:

The quick sort algorithm is applied recursively to the sub-arrays formed by partitioning.

4. In-place Sorting:

Quick sort sorts the elements within the same array, making it memory efficient.

Implementing Quick Sort in C

Step 1: Partitioning the Array

The partitioning function reorders the array based on the pivot, placing smaller elements to the left and larger elements to the right of the pivot.

Step 2: Quick Sort Recursion

Once the array is partitioned, the quick sort function recursively sorts the two sub-arrays.

Quick Sort Code in C

Code Breakdown:

1. swap Function:
   • Swaps two elements in the array, necessary for rearranging elements during partitioning.
2. partition Function:
   • Selects a pivot (in this case, the last element of the array) and rearranges elements so that smaller values come before the pivot and larger values come after.
   • Returns the index of the pivot element after partitioning.
3. quickSort Function:
   • Recursively sorts the left and right sub-arrays formed by partitioning.
4. printArray Function:
   • Prints the array to visualize the sorting process.

Sample Output:

Practical Example: Sorting a List of Test Scores

Consider modifying the code to sort an array of student test scores:

This will output the sorted test scores in ascending order.

Conclusion

Quick sort is a highly efficient sorting algorithm commonly used in C programming. It efficiently sorts arrays using the divide-and-conquer approach, requiring minimal additional memory as it is an in-place sorting algorithm. By recursively partitioning and sorting sub-arrays, quick sort achieves an average time complexity of O(n log n), making it suitable for large datasets. Mastering the quick sort algorithm in C provides a solid foundation for solving a wide range of sorting problems.