find-strong-numbers-range()

Step 1: Understanding the Problem

A strong number is a special number whose sum of factorial of digits is equal to the original number. For instance, 145 is a strong number since 1! + 4! + 5! = 145. The goal is to write a function to find such numbers within a given range.

// Initial function declaration

func findStrongNumbersInRange(start: Int, end: Int) -> [Int] {
}

Step 2: Calculate the Factorial

First, we need a helper function to calculate the factorial of a number. This can be done with a simple loop.

// Including the factorial function in our main function

func findStrongNumbersInRange(start: Int, end: Int) -> [Int] {
    func factorial(_ num: Int) -> Int {
        var fact = 1
        for i in 1...num {
            fact *= i
        }
        return fact
    }
}

Step 3: Check if a Number is Strong

Next, we need to check if a number is strong. Convert the number to a string, calculate the factorial for each digit and sum them up. If the sum equals the original number, it is a strong number.

// Adding isStrong function

func findStrongNumbersInRange(start: Int, end: Int) -> [Int] {
    func factorial(_ num: Int) -> Int {...}

    func isStrong(_ num: Int) -> Bool {
        let digits = String(num).compactMap { Int(String($0)) }
        let sum = digits.map { factorial($0) }.reduce(0, +)
        return sum == num
    }
}

Step 4: Finding Strong Numbers in a Range

Finally, we'll iterate through the given range and use the isStrong function to find strong numbers. The numbers will be collected into an array and returned by the function.

// Final Swift function to find strong numbers in a range

func findStrongNumbersInRange(start: Int, end: Int) -> [Int] {
    func factorial(_ num: Int) -> Int {...}

    func isStrong(_ num: Int) -> Bool {...}

    var strongNumbers: [Int] = []
    for i in start...end {
        if isStrong(i) {
            strongNumbers.append(i)
        }
    }
    return strongNumbers
}

Conclusion

This function efficiently finds all the strong numbers in a given range. The helper functions factorial and isStrong assist in breaking the problem into smaller, solvable steps.