Mastering QuickSort in SwiftUI: Building a QuickSort Visualiser ????

Hey all! Today, I’ve provided an iOS visualisation of a really common sorting algorithm and some information that may help you understand what’s going on.

QuickSort is a divide-and-conquer algorithm that efficiently sorts data by partitioning arrays into smaller sections. Understanding it is key for anyone serious about software engineering, and here’s a quick guide to refresh your memory.

Why care about Quick Sort?

QuickSort is great for general purpose sorting. It’s a great algorithm for sorting in most cases, especially when the dataset is large and performance is key.

Because it’s in-place, QuickSort is preferred when memory is limited and there are memory constraints.

?? Here's the link to the Demo on Github if you'd like a play around with it yourself!

https://github.com/hanisa1/QuickSortVisualisation/tree/main

How It Works

• Pick a Pivot: Choose an element from the array (commonly the last or middle element).
• Partition: Re-arrange the array so that all elements less than the pivot come before it, and all elements greater come after it.
• Recursively Sort: Apply the same logic to the subarrays on both sides of the pivot.
• Combine: The base case is reached when the subarrays have one or zero elements—at that point, everything is sorted.

Time Complexity

• Best Case: O(n log n) (Balanced partitions)
• Average Case: O(n log n)
• Worst Case: O(n^2) (Happens when the pivot is poorly chosen and leads to unbalanced partitions)

Space Complexity

• O(log n) for the stack space used by recursion (in-place sorting)

QuickSort Implementation in Swift

Here’s a Swift implementation using recursion to give you a run down of what it will look like.

func quickSort(_ array: [Int]) -> [Int] {

    guard array.count > 1 else { return array }
    
    let pivot = array[0]
    
    let less = array.filter { $0 < pivot }
    let equal = array.filter { $0 == pivot }
    let greater = array.filter { $0 > pivot }
    
    return quickSort(less) + equal + quickSort(greater)
}

// Example usage

let unsortedArray = [10, 7, 8, 1, 9, 5]
let sortedArray = quickSort(unsortedArray)
print(sortedArray)          

Strengths and Weaknesses

Mastering QuickSort is an essential step for anyone looking to level up their algorithms and data structures skills. Understanding this algorithm will make you a stronger, more capable developer.

Hope you enjoyed this one,

Hanisa ??