Stack overflow while using recursive function

Question

I am trying to do a simple coding challenge that requires me to do the following:

You are given n, return an array ans, composed in such way:

`ans = [n, n - 5, n - 10, ... , m, m + 5, ... , n - 5, n]`, where m stands for the first non-positive integer obtained by subtractions.

Try to solve it without any loop.

Example

For n = 25, the output should be

listWithoutLoop(n) = [25, 20, 15, 10, 5, 0, 5, 10, 15, 20, 25].

I have done this code:

int[] listWithoutLoop(int n)
{
    List<int> test = new List<int>();

    if (test.Count > 2 && test[test.Count - 1] == n)
        return test.ToArray();

    if (n <= 0)
    {
        test.Add(n + 5);
        return listWithoutLoop(n + 5);
    }
    else
    {
        test.Add(n - 5);
        return listWithoutLoop(n - 5);
    }
}

But I keep getting a stack overflow when running it. Is recursion supported by c#? If so, how to prevent getting a stackoverflow exception when running it?

Answer 1

To simplify, I splitted the function to add up and add down separately (it's always better to have simple and understandable code at all times)

    static void Main()
    {
        int n = 20;
        int interval = 5;

        List<int> list = new List<int>();
        AddDown(list, n, 0, interval);
        AddUp(list, 0, n, interval);

        int[] arrInt = list.ToArray();

    }

    static void AddDown(List<int> list, int currentNumber, int targetNumber, int interval)
    {
        if(currentNumber > targetNumber)
        {
            list.Add(currentNumber);
            AddDown(list, currentNumber - interval, targetNumber, interval);
        }
    }

    static void AddUp(List<int> list, int currentNumber, int targetNumber, int interval)
    {
        if (currentNumber <= targetNumber)
        {
            list.Add(currentNumber);
            AddUp(list, currentNumber + interval, targetNumber, interval);
        }
    }