Swift Coding Test Course, Radix Sort

Hello! Today, we will discuss the Radix Sort algorithm using Swift. Radix Sort is an efficient algorithm that sorts by grouping similar numbers together, primarily used for sorting a set of integers.

Overview of Radix Sort

Radix Sort is a comparison-based sorting algorithm that sorts numbers or strings by breaking them into digits. Radix Sort works as follows:

• It decomposes the given number into specific digit places.
• It sorts starting from the least significant digit (LSB).
• It repeats this process for higher digit places.

Radix Sort is a stable sorting algorithm, and its average and worst-case time complexity is O(nk), where n is the number of elements and k is the maximum number of digits.

Problem Description

Now let’s solve the following problem using Radix Sort.

Problem:

Sort the following integer array in ascending order using the Radix Sort algorithm:

[170, 45, 75, 90, 802, 24, 2, 66]

Solution

To solve the problem, we will implement the Radix Sort algorithm step by step. We will write the code using pre-defined functions and structures in Swift.

Step 1: Separating by Digit Places

As the first step of Radix Sort, we separate based on each digit place. To perform this task, we will create a function to extract digits according to their place value.

func getDigit(number: Int, digitIndex: Int) -> Int {
    return (number / Int(pow(10.0, Double(digitIndex)))) % 10
}

Step 2: Implementing the Radix Sort Algorithm

Now let’s implement the complete Radix Sort algorithm. We need to create an array to group by digit places and sort accordingly.

func radixSort(array: [Int]) -> [Int] {
    let maxNumber = array.max() ?? 0
    let maxDigits = String(maxNumber).count
    
    var sortedArray = array
    
    for digitIndex in 0..

func countingSort(array: [Int], digitIndex: Int) -> [Int] {
    let countArraySize = 10
    var countArray = [Int](repeating: 0, count: countArraySize)
    var outputArray = [Int](repeating: 0, count: array.count)
    
    for number in array {
        let digit = getDigit(number: number, digitIndex: digitIndex)
        countArray[digit] += 1
    }
    
    for index in 1..

let unsortedArray = [170, 45, 75, 90, 802, 24, 2, 66]
let sortedArray = radixSort(array: unsortedArray)

print("Sorted array: \(sortedArray)")