Recursion Sequence

Question

I am trying to write a program that checks if there is a sequence in an array using Recursion {2,4,6,8} would return true while (2,4,6,5} would return false. This is what I have so far... TIA

private static boolean arrPattern(int[] arr)
{
    int sequence =arr[1]- arr[0]; 

    for (int i=1;i<arr.length;i++)
        for(int j=2;j<arr.length;j++)
    {
        if (sequence == (arr[j]- arr[i]) & arr.length>0)
        {
            send the subarray (recursive)
        }
        else if (j-i !=sequence)
                     return false;
                    else
            return true;
    }

}

As you can tell I am not sure how to send a subarray to the method again. I believe I have the basic idea down just need to figure out that last part.

I know you can do this simply with having a arraylist instead of a simple array but I want to use an array to solve this.

Tripp Kinetics · Accepted Answer · 2014-06-05 15:53:08Z

4

You can do this by passing an array and a start argument:

private static boolean arrPattern(int[] arr)
{
    return arrPattern(int[] arr, 0);
}

private static boolean arrPattern(int[] arr, int startpos)
{
    ...
}

Pass startpos + 1 in your recursive call, and then check whether startpos is at the end.

answered Jun 5, 2014 at 15:53

Tripp Kinetics

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Ivaylo Strandjev · Accepted Answer · 2014-06-05 15:54:41Z

1

Instead of passing a subarray add two more arguments to you function - the start and end index of the array you are currently considering(or the start index and length). Then when doing recursive call pass the array and new values for these two parameters.

NOTE: As static arrays are passed by a pointer to their first element this will not copy the elements on each call.

NOTE: In fact solving this problem using recursion is harder than solving it using iteration.

answered Jun 5, 2014 at 15:54

Ivaylo Strandjev

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