Swift Recursion

Swift Recursion: In this tutorial, you will learn to create a recursive function; a function that calls itself.

Swift Recursion is the process where a function calls, and the function which calls itself is know as recursive function.

A function that calls itself is known as a recursive function. Also, this method is known as recursion. While creating a recursive function, you should create a condition so the function doesn’t call itself indefinitely (limitlessly).

How recursion works in Swift?

func recurse() {
    //statements
    recurse()
}
recurse()

The figure underneath shows how recursion functions by calling itself again and again.

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In the above flow chart, the recursion executes boundlessly. Nonetheless, almost the entirety of the occasions, you create a recursion that executes until some condition is met.

To forestall infinite recursion, use the recursive call inside the Swift Conditional Statements for example if…else statement.

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Example 1: Print N positive numbers

func countDownToZero(num: Int) {
    print(num)
    if num > 0 {
        countDownToZero(num: num - 1)
    }
}
print("Countdown:")
countDownToZero(num:3)

At the point when you run the accompanying project, the output will be:

Countdown:
3
2
1
0

In the above program, the statement print(“Countdown:”) outputs Countdown: in the console. Also, the statement countDownToZero(num:3) calls the function that takes a parameter Integer.

The statement inside the function countDownToZero() executes and if the condition num > 0 is met, the function countDownToZero() is called again as countDownToZero(num: num – 1).

On the off chance that condition isn’t met, the function call isn’t done and the recursion stops.

Let’s see this in steps

Execution steps

Steps     Function call       Printed num > 0 ?

1              countDownToZero(3)    3              Yes

2              countDownToZero(2)    2              Yes

3              countDownToZero(1)    1              Yes

4              countDownToZero(0)    0              No (Ends)

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Example 2: Find factorial of a number

func factorial(of num: Int) -> Int {
    if num == 1 {
        return 1
    } else {
        return num * factorial(of:num - 1)
    }
}

let x = 4
let result = factorial(of: x)
print("The factorial of \(x) is \(result)")

At the point when you run the accompanying system, the output will be:

The factorial of 4 is 24

How this example works?

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Let’s see this in steps

Execution steps

Steps     Argument passed            Return statement            Value

1              4              return 4 * factorial(of:3)               4 * factorial(of:3)

2              3              return 3 * factorial(of:2)               4 *3 * factorial(of:2)

3              2              return 2 * factorial(of:1)               4 * 3 *2 * factorial(of:1)

4              1              return 1                4 * 3 * 2 * 1

Generally recursion is used as a substitution of iteration when the solution for an issue can be find in around two stages. The initial step searches a solution, if not repeat the process.

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Swift Functions