JavaScript Algorithms - 25 - Quick Sort Solution

Step-by-Step Tutorial: Implementing Quick Sort Algorithm in JavaScript

Step 1: Define the Quick Sort Function

1. Create a function named quickSort with one parameter arr representing the array to be sorted in ascending order.

Step 2: Find the Pivot Element

1. Set the pivot element as the last element of the array: let pivot = arr[arr.length - 1];

Step 3: Divide the Array into Left and Right Arrays

1. Initialize empty arrays for the left and right elements: let left = []; and let right = [];
2. Traverse the array using a for loop, comparing each element with the pivot:
   • If arr[i] is less than the pivot, push it to the left array: left.push(arr[i]);
   • If arr[i] is greater than or equal to the pivot, push it to the right array: right.push(arr[i]);

Step 4: Recursively Sort Left and Right Arrays

1. Call the quickSort function recursively on the left and right arrays, with the pivot element in between:
   • return quickSort(left).concat(pivot, quickSort(right));

Step 5: Implement Base Case for Recursion

1. Add a base case to exit the recursion when the array contains one element:
   • Check if the array length is less than 2 and return the array: if (arr.length < 2) return arr;

Step 6: Test the Quick Sort Algorithm

1. Test the quickSort function with different arrays, including a sorted array and a reverse-sorted array to observe the sorting process.

Additional Information:

• Worst Case Complexity: O(n^2) - Occurs when the array is already sorted, leading to quadratic time complexity.
• Average Case Complexity: O(n log n) - Achieved by recursively dividing the array into smaller arrays, resulting in a more efficient sorting process.
• Space Optimization: It is possible to implement Quick Sort without taking extra space, which is helpful when dealing with space constraints. Check the description for more details or consider using the Merge Sort algorithm as an alternative.

By following these steps, you can successfully implement and understand the Quick Sort algorithm in JavaScript.