Question

I need to write a method which takes in 2 arrays as parameters and returns true if the second array is a sub array of the first and false otherwise. I need to use only recursion without loops but I can use private methods.

So far this is what is have:

public static bool findSequence(char[] findIn, char[] toFind)
{
    return compare(findIn, toFind, num);
}

private static int num = 0;

private static bool compare(char[] findIn, char[] toFind, int num)
{
    for (int i = 0; i < findIn.Length; i++)
    {
        if (toFind[i] != findIn[num])
        {
            num++;
            return false;
        }
    }

    num++;
    return true;
}

Answer 1

You are on the wrong way, since you have to use recursion and to avoid loops, and your code has loops and no recursion. I think that you should try a little bit harder, since this is very useful brain fitness. Anyway, this should work (and even understanding this could be a good exercise 🙂 ):

    public static bool FindSequence(char[] findIn, char[] toFind)
    {
        return FindSequence(findIn, toFind, 0, 0);
    }

    private static bool FindSequence(char[] findIn, char[] toFind, int posInFindIn, int posInToFind)
    {
        if (findIn.Length - posInFindIn < toFind.Length - posInToFind)
            return false;
        if (findIn[posInFindIn] == toFind[posInToFind])
        {
            if (posInToFind == toFind.Length - 1)
                return true;
            else
                if (FindSequence(findIn, toFind, posInFindIn + 1, posInToFind + 1))
                    return true;
        }
        return FindSequence(findIn, toFind, posInFindIn + 1, 0);
    }